My picks would be...
1: Greg Monroe
I don't care what anybody says about this 'newage' leagues, I still think it's extremely important to have a big who is skilled in the post. Greg Monroe is currently averaging 15 points, 10 rebounds and 2 assists in only 29.5 MPG while also shooting 48% from the field and 76% from the foul line.
He's also dependable - he's missed maybe 20 games over his entire 5 year career, and doesn't have a problem with foul trouble (unlike our current bigs).
Monroe's age is another benefit for Boston - at 24 year old he is in the exact same age group as the rest of Boston's young core (Sully, Olynyk, AB, etc), and he's also young enough that even on a max contact (which he would certainly demand) he would still be earning reasonable money.
2. DeAndre Jordan
Next guy I'd go after is DeAndre Jordan. This guy is lacking offensive skill, but he's a dominant force on defence and on the boards. I like to think of him as a younger, more athletic version of Tyson Chandler - the type of player who could anchor a teams defence.
With a front court of Monroe + Jordan and a backup rotation of Sully, Olynyk and Zeller...we'd have one of the deepest front lines in the league...and one that is absolutely full of potential.
Next thing we need (since with ditched Green) is a perimeter scorer. This is going to be the tougher part, because I don't think there's one out there that really fits Boston's plans...and who would actually consider coming here. If we could get Butler then great, but I'm really not convinced he's a #1 option type of guy. Might need to hope for some luck and try to acquire a big time scorer in the draft...
Bradley will do for now at SG - he's inconsistent, but he's good enough on both ends the floor to hold down his position. We really need an improvement at SF and (depending on how Smart develops) PG.