Well, let's see if I can clarify a couple of points.
1) Don't worry about posting millions of questions, go right ahead and we will answer -that's what we are here for.
2) Just because you saw him and scratched his head in the store, it doesn't mean that he trusts you or that he is even comfortable with you (actually, going by the body language you described, he doesn't trust you at all). That process takes several months, actually (dogs will trust any human implicitly but not parrots, you need to win them over).
3) ALL parrots belong on their owner's shoulders unless they are BIG macaws which prefer the arm. No parrot likes to ride a hand or a finger. Mine do it without a problem because they know that I only use this for transporting them from one place to another and, besides, they have all the access to my shoulders, head, lap or whatever part of me they decide to perch on. People who don't want their parrots on their shoulders are not parrot people - it might sound harsh but it's God's truth and the reason for this is that riding their human's shoulder makes them feel safe (high up so predators cannot reach them) and loved (physically close to their human). Besides, how would you go about doing your stuff if the parrot is not on your shoulder? They need soooo many hours of out-of-cage time that if they are not on your shoulder, people would need not only a maid to do their chores but spend boring hours and hours and hours doing nothing -something the parrot would not appreciate, either
4) ALL parrots will step up when on the floor -even the ones that would NEVER do it from any other spot.
5) You should not be rewarding him for stepping up. Young hand-fed birds that trust you would do it on their own so, if you need to bribe, he doesn't trust you yet (the leaning back when you ask him to step up is a dead give-away!) and, if he doesn't trust you yet, you shouldn't be asking (would you insist on picking up a child who doesn't know you and doesn't want to be touched by you to the point that he leans back so as to distance himself from you?). It is, obviously, too early to be asking and you need to win him over. If you take the time to bond with him first, he will want to step up on its own.