IMHO we should look to add in no particular order:
A long ultra athletic big like Larry Sanders. Must be legit 6-11 minimum with shot blocking skills. Doesnt need to be a long range jumpshooter.
A long and athletic wing/guard that can play multiple positions and shoot moderately well. 15ft jumper would be fine. Must be 6-7+ legit in height.
A tough minded combo guard/ball handler that attacks the basket. Oh wait, we have him
Avery Bradley.
A long and tough defensive minded combo forward (legit 6-9) like Tayshawn Prince.
A down and dirty low block player who plays physical defense, carves out space and rebounds. Minimum height 6-10 and can jump.