If you haven't allready, check out:
http://www.exploremaine.org/bike/greenway.html
I rode a good bit of the Maine coast as my first "shakedown" tour a few summers ago (Freeport to Acadia). The cue sheets I printed up from the Maine DOT were pretty good. The coastal towns are kinda nice, but Camden seemed most memorable. There is a state park with camping just north of the center of town. There is a small mountain (in the park) with excellent views of the town&bay. If I recall, there is also camping (commercial), not far from one of the lighthouses near there as well.
There was ample camping available in Acadia when I went (over 4th of July). I "think" they keep a bunch of spots available for walk/bike in folks-not sure though.
If you like to hike, you could hike-a-bike (bike to trails+hide/lock the bike) a bit of the White Mts-and/or bike the Kancamangus hwy as part of your loop. Decent on line resources for hiking the Whites are:
http://appalachia.outdoors.org/bbs/index.cfm (Appalacian Mountain Club BBS)
http://216.234.118.44/ (Views From the Top BBS)
Darrens VFTT is the better of the two.