You said this is your plan:
my plan is to upgrade passing, jump shot and inside shot to respectable this season if i can, and then do 1v1 all of next season when i have more players to train
The superior trainer is enough...But if you want this player to play in U21 you must train him only at core skills in one position
(inside shot,inside def,rebound and block shot)
This player never will play at NT of USA because of his potential
If you want to continue your plan you will do a perfect PF which will not play at NT
So decision is yours