If you want to be realistic about where guys will play the depth chart as of now (assuming rookies are both signed) looks like:
Rondo / House / Pruitt
R. Allen / T. Allen / Giddens
Pierce / xxx / Walker
KG / Powe / Scal
Perk / BBD / O'B
Well I agree there is a whole at SF in the depth chart, Scal and T. Allen will likely split the minutes behind Pierce. Scal will get the call for certain bigger SFs, and TA will get the rest. Last year Ray Allen played 10% of the SF minutes, and he plays smaller than TA imo.
In terms of usage I'd expect the plan is: (ordered by minutes - just rounded to nearest 5):
starters: Pierce (35), Rondo (35), Ray (35), KG (30), Perk (30) - 5 roster spots / 165 minutes
bench: Powe (25), House (20), BBD (10), Tony (10), Scal (10), Pruitt (5), O'B (3) - 7 roster spots / 75 minuts
DNP: Giddens, Walker - 2 roster spots / 0 minutes
That's 14 roster spots and 248 minutes. Obviously things will fluctuate, but its probably a pretty good guess (and I wouldn't mind seeing more of Ray Allen's minutes cut back and going to House and/or Tony - since he seemed to get broken down for that one stretch in the playoffs.) If PErk can't make 30 minutes a game, then BBD gets more run.