When you don't do akusla you do kusala?

For Arahants, all actions are neither Kusala nor Akusala. For normal beings, all intentional actions are Karma. Which means it is either Kusala(wholesome) or Akusala(unwholesome) Karma.

There is no "neutral Karma". But there are actions which are Karmically neutral. They are called Avyaakata.

Avoiding akusala karma is not a kusala karma.

If kusala and akusala karma are two ends of a pencil with an eraser attached, if you did not use the eraser side does not mean you used the other side . In a same way , if you did not do akusala karma, does not mean you did kusala karma.

What you should do

Basically there are 10 kusala karma and 10 akusala karma (I assume that you know them). Avoid akusala karma and do kusala karma.

Note

Doing just kusala karma will not help you achieve nirvana. You must develop your mind to achieve nirvana. But , every kusala karma you do will have consequences, those will be good. In a same way , akusala karma will have bad consequences.

In Sila you abstain from unwholesome physical and vocal actions. This way you avoid more heavier of the bad Karma. When you abstain from all unwholesome vocal and physical action what remain is wholesome vocal and physical action. This is at a very high level of Sila perhaps that of a monk or nun.

When you start you start with Sila as a rule or practice. As you progress you can look at it as the good of oneself and other. [Sedaka Sutta] At a much later stage this at the level of sensation, where by you recognise which sensation make you react in unwholesome ways and abstain from following through with the actions. [Kīta,giri Sutta] This is based on Insight and Wisdom.

The metal unwholesome action are unavoidable if you are not doing meditation. By meditating you can displace unwholesome mental actions with wholesome mental actions.

For more detail explanation from the Suttas see this answer.

A good reference is MN 114 (only source I've found on the web)

Bhikkhus, I say bodily conduct is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other. Verbal conduct is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other. Mental conduct is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other. Arousing of thoughts is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other. The gain of perceptons is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other. The gain of view is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other. The gain of a self is twofold, consisting of that should be practiced and should not be practiced, that too quite different from each other.” ...

On account of what was it said by the Blessed One? When practicing certain bodily conducts [Verbal conducts, Mental conduct ...], if unwholesome states increases and wholesome states decrease such bodily conduct [Verbal conducts, Mental conduct ...] should not be practiced. When practicing certain bodily conducts [Verbal conducts, Mental conduct ...], if unwholesome states decrease and wholesome states increase such bodily conduct [Verbal conducts, Mental conduct ...] should be practiced.

Notes:

• In the translation I have as a book (not english), it says instead of "is twofold, consisting of" "is twofold and either of the one or the other", which is more clear in my opinion
• I've replaced the words merit and demerit in the translation with wholesome/unwholesome states, which is a better translation of the Pali kusalā/akusalā dhammā

Gautama Buddha gave imperative teachings to Sanga (monks) on every 15 days (twice a month).

1. Do not do any bad deed.
2. Do all good deed in complete way (make them complete).
3. Cleanse the mind from impurities.

From this teachings, you can depict not doing any bad deed (Akusala/Parpa) is not necessarily you are doing good deed (Kusala).

For example, when we are talking about five precepts,

1. Not killing any living being perceiving while doing; it is not doing Akusala (killing). But Kusala on this first precept is spreading Metta and Karuna to all living beings. You are practicing Kusala by having positive kindness, wishing all living being to survive in peace and enjoy their lives. In this practice, spreading Metta and Karuna to all living beings is something to be done and not automatic by being law-abiding first precept.

2. No stealing If you don't do stealing (Akusala), you are not practicing offering/donation. Donation/offer is abandoning your possessions and it is also separate deed other than avoiding stealing.

3. Not having affairs with other people's spouse. Even though you make up your mind not to mess up other people relations and partnership, you may have some burning or subtle inner desire to want to mess up. If you don't cleanse your mind from this impurities, you are not breaking third precept but you don't practice third of Buddha's teaching. If you can cleanse your mind from inappropriate sensual desire, you will have fruitful Kusala about this precept.

4. not telling Lie to deceive people. It is apparent that telling no lie is not telling the truth, you still have right to remain silent. Buddha had practiced Sacca parami completely so refrain from telling lie is not enough to practice Kusala.

5. Refrain from drinking intoxicating liquor/wine/fermented drink. You need to have proper meal with comfortable to your metabolism/ability to digest. Awareness/mindfulness is you need to practice so that you won't hurt yourself by eating junks or inappropriate foods while you don't even drink any alcohol.

It is highly recommended that even though you are not doing any Akusala (keeping five precepts above), at least you should review yourself on daily/weekly basic that you should cherish your Sila is clean, not broken. It will make you have peace in mind and acquire concentration. Mindfulness/awareness is plus to your Kusala and it is not automatic.

I think generally speaking you are on the right track. Your question seems very clear to me and your logic is valid.

Don't do akusala, on all levels from coarse - to very subtle, exactly this was my path, this can be your path. You don't need to worry about kusala, as long as you put serious effort in not doing akusala, you will advance.

Now, "serious effort" is very serious. There is akusala hiding inside kusala, and there is kusala hiding inside akusala. So you should be very bold and very brave. I see you are making progress since you joined.