Honestly, training SF's needs more experience and knowledge about the game than you have at this point in time. I'd train PG's and SG's.
I agree with this...however, if he can find a veteran coach to give him some insight as to what is required to train SFs, there is really no better time than in the lower divisions. It won't be as easy to following that training program in the higher divisions. In the lower divisions that are a lot more games each season that you can win with scrubs, and gives your training program a lot more versatility.
And if he starts now, when he gets to higher divisions, he will have the type of players to help him win, that we all covet.