his potential is superstar
you've just answered my question.
It is very important to keep track of potential because let's take his case he will probabil reach about 150k tops beiing on this potential so it's a good margin for a big guy.
So start with Inside Offence until you reach level 10 and the work on his Inside Defence until level 13-14 and would have covered at least this season and the next if all goes to plan you could get 14 on both until the end of next season.
I recommend you have a trainer level 5 but i think you can pull this off with level 4 as well.
After this you can work on his Rebounding and on his secondaries as well.
You should have a decent big men when he is about 22 and you should buy another player with almost the same potential and skills because it will be wise to train 2 players at least at the same time.