What was the stance of Arius on John 1:1?

St. Thomas Aquinas discusses various errors of Arius and his followers in his Commentary on Chapter 1 of Gospel of John that are connected to Prologue of Gospel of John. If Arius had something to say on that part of Gospel of John it is very reasonable to believe that Aquinas would mention it. Aquinas does not mention Arius in commentary on John 1:1, however he mentions him in commentary on John 1:2.

Aquinas writes (in commentary on John 1:2):

The Arians were able to draw out another error from the above. They think that the Son is less than the Father because it says below (14:28): “The Father is greater than I” And they say the Father is greater than the Son both as to eternity and as to divinity of nature. And so to exclude this the Evangelist added: He was in the beginning with God. For Arius admits the first clause, In the beginning was the Word, but he will not admit that principium should be taken for the Father, but rather for the beginning of creatures. So he says that the Word was in the beginning of creatures, and consequently is in no sense coeternal with the Father. But this is excluded, according to Chrysostom, by this clause, He was in the beginning, not of creatures, but in the beginning with God, i.e., whenever God existed. For the Father was never alone without the Son or Word, but He, that is, the Word, was always with God.

Again, Arius admits that the Word was God, but nevertheless inferior to the Father. This is excluded by what follows. For there are two attributes proper to the great God which Arius attributed solely to God the Father, that is, eternity and omnipotence. So in whomever these two attributes are found, he is the great God, than whom none is greater. But the Evangelist attributes these two to the Word. Therefore, the Word is the great God and not inferior. He says the Word is eternal when he states, He was in the beginning with God, i.e., the Word was with God from eternity, and not only in the beginning of creatures (as Arius held) , but with God, receiving being and divinity from him. Further, he attributes omnipotence to the Word when he adds, Through him all things came into being.

Later Aquinas writes:

Eunomius declared that the Son is entirely unlike the Father. The Evangelist rejects this when he says, and the Word was God. Finally, Arius said that the Son was less than the Father. The Evangelist excludes this by saying, He was in the beginning with God, as was explained above.

Aquinas later continues:

The first clause, All things were made through him, is used to show three things concerning the Word. First, according to Chrysostom, to show the equality of the Word to the Father. For as stated earlier, the error of Arius was rejected by the Evangelist when he showed the coeternity of the Son with the Father by saying, “He was in the beginning with God.” Here he excludes the same error when he shows the omnipotence of the Son, saying, All things were made through him. For to be the principle of all the things that are made is proper to the great omnipotent God, as the Psalm (134:6) says, “Whatever the Lord wills he does, in heaven and on earth.”Thus the Word, through whom all things were made, is God, great and coequal to the Father.

He mentions him later in commentary (on the Prologue of Gospel of John), but for that you can just search "Arius" on the page here and see all places where Aquinas mentions him (in commentary on the Prologue of Gospel of John.)

I do not know whether this answers your question but I think it explains Arius stance on Prologue of Gospel of John.

Further Support

It seems that Arius would interpret words "and the Word was God" meaning that Christ was so perfect (yet inferior to God and not God himself) that he can reasonably be denoted as God. For Christ, in Arius stance, would be greater than inanimate matter, plants, animals, men and angels. It seems that for Arius, he would be so great as to be "almost" as true God (but as Aquinas says above, for Arius he lacks eternity and omnipotence and thefore would not be equal to God). Thefore, it seems that Arius would comment on the passage "and the Word was God" by saying that word "God" should here be understood not in the strict sense, but only to convey the point that he was most perfect creature of God and because he was most similar to God he himself was called God.

I think you could hardly make a better case for Arius. However, his heresy was refuted long time ago (you can find link to Aquinas's refutation of Arius arguments in my answer on this question).

I also found two works that touch upon our discussion.

1. St. Athanasius - Deposition of Arius

Now those who became apostates are these, Arius, Achilles, Aeithales, Carpones, another Arius, and Sarmates, sometime Presbyters: Euzoïus, Lucius, Julius, Menas, Helladius, and Gaius, sometime Deacons: and with them Secundus and Theonas, sometime called Bishops. And the novelties they have invented and put forth contrary to the Scriptures are these following:— God was not always a Father , but there was a time when God was not a Father. The Word of God was not always, but originated from things that were not; for God that is, has made him that was not, of that which was not; wherefore there was a time when He was not; for the Son is a creature and a work. Neither is He like in essence to the Father; neither is He the true and natural Word of the Father; neither is He His true Wisdom; but He is one of the things made and created, and is called the Word and Wisdom by an abuse of terms, since He Himself originated by the proper Word of God, and by the Wisdom that is in God, by which God has made not only all other things but Him also. Wherefore He is by nature subject to change and variation as are all rational creatures. And the Word is foreign from the essence of the Father, and is alien and separated therefrom. And the Father cannot be described by the Son, for the Word does not know the Father perfectly and accurately, neither can He see Him perfectly. Moreover, the Son knows not His own essence as it really is; for He is made for us, that God might create us by Him, as by an instrument; and He would not have existed, had not God wished to create us. Accordingly, when some one asked them, whether the Word of God can possibly change as the devil changed, they were not afraid to say that He can; for being something made and created, His nature is subject to change.

3 Now when Arius and his fellows made these assertions, and shamelessly avowed them, we being assembled with the Bishops of Egypt and Libya, nearly a hundred in number, anathematized both them and their followers. But Eusebius and his fellows admitted them to communion, being desirous to mingle falsehood with the truth, and impiety with piety. But they will not be able to do so, for the truth must prevail; neither is there any communion of light with darkness, nor any concord of Christ with Belial. For who ever heard such assertions before ? Or who that hears them now is not astonished and does not stop his ears lest they should be defiled with such language? Who that has heard the words of John, In the beginning was the Word John 1:1, will not denounce the saying of these men, that there was a time when He was not? Or who that has heard in the Gospel, the Only-begotten Son, and by Him were all things made , will not detest their declaration that He is one of the things that were made. For how can He be one of those things which were made by Himself? Or how can He be the Only-begotten, when, according to them, He is counted as one among the rest, since He is Himself a creature and a work? And how can He be made of things that were not, when the Father says, My heart has uttered a good Word, and Out of the womb I have begotten You before the morning star ? Or again, how is He unlike in substance to the Father, seeing He is the perfect image and brightness Hebrews 1:3 of the Father, and that He says, He that has seen Me has seen the Father ? And if the Son is the Word and Wisdom of God, how was there a time when He was not? It is the same as if they should say that God was once without Word and without Wisdom. And how is He subject to change and variation, Who says, by Himself, I am in the Father, and the Father in Me , and I and the Father are One ; and by the Prophet, Behold Me, for I am, and I change not ? For although one may refer this expression to the Father, yet it may now be more aptly spoken of the Word, viz., that though He has been made man, He has not changed; but as the Apostle has said, Jesus Christ is the same yesterday, today, and forever. And who can have persuaded them to say, that He was made for us, whereas Paul writes, for Whom are all things, and by Whom are all things ?

4 As to their blasphemous position that the Son knows not the Father perfectly, we ought not to wonder at it; for having once set themselves to fight against Christ, they contradict even His express words, since He says, As the Father knows Me, even so know I the Father John 10:15 . Now if the Father knows the Son but in part, then it is evident that the Son does not know the Father perfectly; but if it is not lawful to say this, but the Father does know the Son perfectly, then it is evident that as the Father knows His own Word, so also the Word knows His own Father Whose Word He is.

2. St. Alexander of Alexandria - Epistles on the Arian Heresy and the Deposition of Arius.

4 But that the Son of God was not made from things which are not, and that there was no time when He was not, the evangelist John sufficiently shows, when he thus writes concerning Him: The only-begotten Son, who is in the bosom of the Father. John 1:18 For since that divine teacher intended to show that the Father and the Son are two things inseparable the one from the other, he spoke of Him as being in the bosom of the Father. Now that also the Word of God is not comprehended in the number of things that were created from things which are not, the same John says, All things were made by Him. For he set forth His proper personality, saying, In the beginning was the Word, and the Word was with God, and the Word was God. All things were made by Him; and with out Him was not anything made that was made. John 1:1-3 For if all things were made by Him, how comes it that He who gave to the things which are made their existence, at one time Himself was not. For the Word which makes is not to be defined as being of the same nature with the things which are made; since He indeed was in the beginning, and all things were made by Him, and fashioned from things which are not.Moreover, that which is seems to be contrary to and far removed from those things which are made from things which are not. For that indeed shows that there is no interval between the Father and the Son, since not even in thought can the mind imagine any distance between them.But that the world was created from things which are not, indicates a more recent and a later origin of substance, since the universe receives an essence of this sort from the Father by the Son. When, therefore, the most pious John contemplated the essence of the divine Word at a very great distance, and as placed beyond all conception of those things that are begotten, he thought it not meet to speak of His generation and creation; not daring to designate the Creator in the same terms as the things that are made. Not that the Word is unbegotten, for the Father alone is unbegotten, but because the inexplicable subsistence of the only-begotten Son transcends the acute comprehension of the evangelists, and perhaps also of angels.

Later, we have:

3 Since those about Arius speak these things and shamelessly maintain them, we, coming together with the Bishops of Egypt and the Libyas, nearly a hundred in number, have anathematized them, together with their followers. But those about Eusebius have received them, earnestly endeavouring to mix up falsehood with truth, impiety with piety. But they will not prevail; for the truth prevails, and there is no communion between light and darkness, no concord between Christ and Belial.2 Corinthians 6:14 For who ever heard such things? Or who, now hearing them, is not astonished, and does not stop his ears that the pollution of these words should not touch them? Who that hears John saying, In the beginning was the Word, John 1:1 does not condemn those who say there was a time when He was not? Who that hears these words of the Gospel, the only-begotten Son; John 1:18 and, by Him were all things made, John 1:3 will not hate those who declare He is one of the things made? For how can He be one of the things made by Him? Or how shall He be the only-begotten who, as they say, is reckoned with all the rest, if indeed He is a thing made and created? And how can He be made of things which are not, when the Father says, My heart belched forth a good Word; and, From the womb, before the morning have I begotten You? Or how is He unlike to the substance of the Father, who is the perfect image and brightness of the Father, and who says, He that has seen Me has seen the Father? John 14:9 And how, if the Son is the Word or Wisdom and Reason of God, was there a time when He was not? It is all one as if they said, that there was a time when God was without reason and wisdom. How, also, can He be changeable and mutable, who says indeed by Himself: I am in the Father, and the Father in Me, John 14:10 and, I and My Father are one; John 10:30 and by the prophet, I am the Lord, I change not? Malachi 3:6 For even though one saying may refer to the Father Himself, yet it would now be more aptly spoken of the Word, because when He became man, He changed not; but, as says the apostle, Jesus Christ, the same yesterday, today, and forever. Hebrews 13:8 Who has induced them to say, that for our sakes He was made; although Paul says, for whom are all things, and by whom are all things? Hebrews 11:10.

Edit 2.

We read on page 101 of Arius: Heresy and Tradition:

(vi) Again, he has presumed to say that the Word is not true God (theos alithinos). "He may be called 'God' but he is not 'true God'. It is only by participating in grace, like all others, that he too is called by the name 'God'. All beings are, in respect of their substance (kat' ousian), alien to God and unlike him (xenon kai anomoion); and so too the Word is entirely different from and unlike the Father's substance and property (idiotitos). He is 'proper' to (idios) [the class of] made and created things and it is to this that he belongs.