It must include IS, ID, SB, any ideal skills for an inside man.
I think rebounding is way more important than SB. SB adds way too much to the players' salary given how useful it is. Personally I wouldn't bother to train SB at all, but I might be a bit extreme. I think it's safe to say that the core skills for all big men is IS, ID and RB, with shotblocking being secondary at best.