My guess is that someone is going to offer Marquis Daniels more than $2.5 million and will likely be a contending team. I also don't see where they get the money to pay Nate. Finally, Glen Davis will never be a top-level NBA 6th man.
My predictions:
Daniels will be offered most of the MLE by the Spurs (in warm, income tax-free Texas), and he'll take it.
Glen Davis will have a career as a solid rotation big man, but will be a hustle player, not an impact player, due to inherent limits in height, length, and athleticism. Eventually a team that signs him to a long contract will regret it as it becomes more expensive in the out years, and his play plateaus.
The Celtics resign Nate for 2-3 years (possible 3rd year an option or partially guaranteed) at 4 million/year plus incentives (within range of his current salary and appropriate for a backup), becoming a drive/dish team based on PG penetration from Rondo and Nate and jumpers from Pierce and Ray, and a 1-4 pick/roll team with KG, BBD, and Sheed.
The Celtics do not use the full MLE this summer, as they don't find a player who would make them that much better, and instead begin trying to develop assets/young players alongside the aging 3.
TA and Scal are invited back on minimum contracts, and eventually accept them.
Perk turns down an extension this summer, and gets shopped at next year's deadline.