Quick note up front, I'm planning to edit this to add further info when I have time to break out my Berkhof and/or other relevant texts. But here's a quick response:

I think part of the problem here is wikipedia. You are getting confused by the wording of wikipedia, which is confusing, and not exactly accurate.

Supralapsarianism teaches, essentially, that God determined to create for himself a people to redeem and a people to judge (if you accept double predestination). Once he had made this decision he then determined how to accomplish this through the creation of a people who would fall and be redeemed by Christ. To use a logic order as you have above, it would be formulated as:

Supralapsarianism (modified)

1. the election of some men to salvation in Christ (and the reprobation of the rest of sinful mankind in order to make known the riches of God's gracious mercy to the elect)
2. the decree to apply Christ's redemptive benefits to the elect sinners
3. the decree to redeem the elect sinners by the cross work of Christ
4. the decree that men should fall
5. the decree to create the world and men

Infralapsarianim teaches, on the other hand, that God determined to create people, determined that these people would fall and that he would redeem them through his Son. Again, to use the logic order it should be formulated:

Infralapsarianism

1. the decree to create the world and (all) men
2. the decree that (all) men would fall
3. the election of some fallen men to salvation in Christ (and the reprobation of the others)
4. the decree to redeem the elect by the cross work of Christ
5. the decree to apply Christ's redemptive benefits to the elect

Keep in mind that in both views God is proactively determining each step. None are reactionary but rather the will of God in eternity. The debate is purely over the logical order of God's thought and, therefore, necessarily speculative.

Here's a much better source than wikipedia to help clarify these terms: https://www.monergism.com/thethreshold/articles/onsite/qna/superinfra.html

I may be misunderstanding parts of your questions, so I apologize if my answer just isn't relevant.

Supralapsarianism

how someone thinking to choose something from a total sum while there isn't preceding thinking that there is something to choose from?

This is an easy thing to do. A simple example: rather than saving humans, lets consider the outcome of catching 1 out of 3 falling paper balls.

Here's the supralapsarianist's thought process:

1. I want to catch 1 falling ball and let 2 drop.
2. I will create 3 paper balls, knowing which 1 I want to catch
3. I will now drop all 3 balls
4. I will then catch the 1 that I planned on catching.

Infralapsarianism

Unfortunately, I don't understand your question here.. but my understanding of how this would apply to the above example:

1. I want to create 3 paper balls
2. I will then drop those paper balls (not because I want to save 1, but for some other reason).
3. Since these balls are going to drop, I should save 1 of these balls.

Hope this helps, but don't take these simple examples as completely depicting each of these ideas! They are just my attempt at simplifying the concepts

This question strikes at a more fundamental issue in the discussion of creation in general. In order to create any actual thing, God must first think of the thing he creates. Therefore, this "idea" of the thing created is preexistent to the thing itself. For example, in order to create Paul, God must first have the idea of Paul which precedes Paul's creation. 

How would such a thing be preexistent if it exists contingently upon God? Because God's thoughts and speech are creative extensions from himself. Paul is not an immutable "part" of God's divine unchangeable substance or this would give rise to Pantheism since the whole universe could be said to exist in this way and so the whole universe would conceptually be identical with God. Rather, God's thoughts, and therefore his will, is produced from himself, but not identical with himself. 

This solves the problem of explaining the way the God can have intentions for people who have not yet been created, as indeed the Bible says:

3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, 4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love 5 he predestined us for adoption as sons through Jesus Christ, according to the purpose of his will, 6 to the praise of his glorious grace, with which he has blessed us in the Beloved. - Ephesians 1:3-6

In this context, we can discuss the logical order of the decrees in a context where it makes sense to speak of Paul's election prior to Paul's creation.

Likewise, if you accept that God's logically first decree is to produce two kinds of people, elect and reprobate, then it makes sense for creation to come logically after. A potter has the ultimate intention of storing a jug of water, so he decides to create a certain kind of pot. All of his logic goes into deciding what kind of pot he wants to make and when he is finished, he begins to make that pot. The decree to create affects all these hypothetical potentialities of pots which are never actualized as well as the actual pot which exists only after this logical step.