We aren't getting a starting center, not with what we have left for trade options or salary exemptions. Sully will be in the rotation, probably the first big off the bench (KG and Bass starting), with Jeff Green getting some minutes at PF and Chris Wilcox in the mix as well.
Since we now have pretty good depth in the backcourt, I'd really like to see them use the BAE on another big, another guy who's got a little beef in his backside and six fouls that you'll remember. I think Melo can develop into that player, but you really can't have too many bigs around.
But, as to the OP... the C's have quietly rebuild a pretty decent, youngish core. Pierce, KG, and Terry are all on the older side, but you've got a nice balance of youngish vets (Rondo, Lee, Green, Bass, Wilcox) and some interesting very young players (AB, Sully, Melo). They're still lacking a youngish go-to scorer, but not every team in the league can have a Kevin Durant.
The team isn't going to be as reliant on guys like JO and Shaq and Ray Allen and 'Sheed and other guys on the last legs of their careers.