Celtics need Ray back as they need KG. He was great last year before the ankle problems, and he'll be great next year. Celtics can sign him for 2 years/13M, with no-trade clause. It's not clear if KG/Pierce/Ray will be playing for 1 or 2 or 3 more years, I bet they'll decide after every season.
Celtics need to use their cap space on their own free agents. Then, they can use MLE or even a sign & trade of Bass if he wants BBD money (too much IMO) to get a useful veteran or young player (Kaman, Camby, Ilyasova, Beasley, Mayo, Jason Thompson...) with no more than 2 years left, getting flexibility on the 2014 summer.
Sign Ray for two years, sign Jeff Green for 1 year at reasonable money/2 years at slightly below MLE with team option and insurance for health issues. Then see what Bass will command, if he doesn't want 2 years/9 MIL then try to sign & trade him. If Stiemsma takes QO, ok, if he gets more elsewhere, let him go.
Bring back Pietrus for little money. Give Sean Williams a chance to make the team through training camp. Sign the rookies. That's something like:
Rondo/Moore
Avery/Ray/Pietrus
Pierce/Green/Joseph(?)
Bass(?)/Sullinger/JJJ
KG/Melo/Stiemsma(?)/Sean Williams(?)
If Bass is gone, try to bring a useful player at any position, we need players who can play and give the Big 3 a lot of rest in the Regular Season. Cut/trade the non-guaranteed guys if you need to bring a veteran at any point.