I don't think there's enough minutes and roster space to add bench shooters.
IT, Bradley, and Smart are going to take up nearly all the minutes at guard. Maybe one of our rookies or 2nd year players can challenge Smart for minutes.
Durant will play about 36 minutes at the 3 leaving Crowder about 12.
Crowder will be on the court with Durant let's say about 20 mpg. That leaves about 28 mpg left at the 4. Combine that with the 5 and that's about 76 minutes left for Horford and Olynyk. Figure 30 minutes for Horford and 20 for Olynyk and we have 26 minutes left.
I haven't even mentioned Brown who will spend time on the court with Crowder and Durant while Horford and Olynyk are manning the 5. That's all the time there is. Of course Mickey and Zizic (if he comes over) will be fighting for minutes.
As far as shooting, we'll have enough after adding Durant. I do think we need a backup center, but that person will need to take the vet min and can't expect to get regular minutes or play every game. Anderson or Stoudamire would nice, but they might have better opportunities. I wouldn't object to old Perk.