Looking at the list at hoopsworld, most of the PF's that I would like the C's should have are Restricted FA's but I hope they'd go and at least give a look for these names.
Jason Thompson
Marreese Speights
Anthony Randolph
Darrel Arthur
JJ Hickson
Darrell Arthur would be a steal if you can get him for cheap because of his injury. He'd be a perfect replacement for Bass.
Speights and Jason Thompson will probably get more than they deserve, but Anthony Randolph or Beasley (is he a FA this summer?) don't play a lot for the Wolves, and I love to have them in Green.
About the draft, Royce White will be a 3/4 in the league, and I can't see Ainge drafting Melo or Ezeli with his first round picks. My guess is he drafts a big forward (Quincy Miller/Royce White/Terrence Jones...ok pipedream) and a guard with the other first rounder. Then he finds yet another undersized PF in the 2nd round.
No to Humphries at more than 4-5 million a year. He looks good in Sportscenter, but he's not that good.
Kaman for 1 year could be a great fit, if the veterans (hopefully) come back for another run. He's not a great defender, but if he wants to, he can do good things. If he doesn't pan out, you can pack him at the trade deadline.
Wilcox and Stiemmsma deserve a roster spot for limited money, health could do wonders on both. And either Hollins or Sean Williams could be end-of-the-bench options if the Celtics can't find better players.