this draft class is going to be very weak as far as big men go. The only true post players that are top 20 talents are Kanter, Sullinger, and Trey Thompkins. We'd have to have a lottery pick to keep our selection so the only guys we could really look at are Kanter and Sullinger. But both of those guys will be top 5ish picks so we'd have to suck pretty massively to get either one. Even still, Sullinger is a pure PF while Kanter doesn't have ideal size for an NBA Center himself.
If we keep our pick, Harrison Barnes should be our target. He seems to be falling due to his lackluster play thus far, and if he's available in the 8-12 range we should go for it. Terrence Jones would be my secondary choice for this slot, though I personally don't like him that much. Barnes can fill in at either spot for Jack/Crash and make both of them equally expendable. Jones is more of a SF/PF combo so he's a bit more post-oriented than Barnes. Kyrie Irving would trump both of them if he declared, but I have doubts that he will--with his injury.
As for late first/early second rounders, we should have four targets, two guards and two big men: Nolan Smith, Klay Thompson ... and JaJuan Johnson, Keith Benson.