I think that all skills which must be trained in wrong position should be trained first. That will keep salary low and it's possible in lower divisions only. In my country that kind of training is quite common and possible in DIII and DIV only. DII level competition is quite hard and thus training on wrong position is giving all too much favor for opponents. Training in that order will also make it possible that some higher level teams can buy your player later if you decide to sell your "star". Of course also main skills must be adequate for corresponding division level. So do not count on that some team in NBBA will buy your player and continue training towards NT. Training to NT level is always a sacrifice for a team.
Then some words about potential. I have trained some superstar players from 18 to 25 = 7 seasons without any caps. It's question of balance and skill skill distribution. So now counting on that player is ATG and can be trained a lot longer is definetly true. But I have also one MVP player trained for age of 27 and no cap either. So I'm trying to say that training will slow down quite much because of age, you necessarily never need ATG potential, HoF is enough and in some cases also MVP - depends on skill distribution you are aiming. For very balanced players it clear that HoF is definetly enough and you can train until age of 30. If your player is behind in skills already at the age of 20, he will be also behind in age of 30.
If your focus is to get NT player, I think only way is to make some kind of specialist or utilize his ATG potential and make it way over any limits some skills and be prepared to pay huge salaries, but both ones are risky and there is no any guarantees that he will make NT level.
Training for money and own team has seldom same targets than NT team has.
Nothing new in my post, just some thoughts. It has been pleasure to read ideas and discussions about reasonable skill distribution. Only thing I have some thoughts is RB.....you don't need RB if your shooting% is high enough. And you can still get some rebounds with extremely low RB...so I'm not quite sure that RB is right way to go either. It's one of the most expensive skills.