We will need to get good defensive bigs. In the pool, only Kai (who has improved on D) and AJ are decent in the defensive bigs department. Carl has a ways to go, and he's probably a system defender at best. Best candidates I can find so far are Kemark Carino and maybe Clifford Jopia.
If we can't find a defensive big, we need a good defensive wing like Will Navarro or even guys like Jacob Bayla so that we don't allow easy penetration whenever we have a lineup that has neither Kai nor AJ on the floor. In the pool, Dwight and JB are the only wings that have shown to be able to guard their man. I don't know if Oftana and Malonzo can stop dribble penetration on their own, although they can rotate when needed. Whenever Oftana, Malonzo, or Quiambao is the 3, I think we'll need Kai and/or AJ on the floor.
Those are the two holes I'm seeing on defense. An extra defensive big and/or wing in case neither Kai nor AJ are on the floor. Yes, we'll defend on scheme, but we need the personnel. Otherwise, easy baskets for the opponent.