any advice as to the best harbor to spend July 4th weekend around there?
We usually find a quiet cove somewhere. And there are a lot of them. If you don't already have it get Taft's Cruising Guide to the Maine Coast
If you want to see fireworks, Stonington usually has a good display over the harbor if no fog. There are plenty of anchorages in and among the islands around Merchants Row that would give a fairly good view. Stonington harbor itself tends to be rocky rolly and moorings are scarce. If you want to be at a dock, call Billings Diesel and Marine in Stonington in advance and see if you can reserve a slip. They only have a few.
Rockland may have fireworks. Call the town office or chamber of commerce to see. Reserve a mooring or slip space from the harbor master.
Camden looks like they will have fireworks. Nice inner harbor. Get resevations for a float in the inner harbor from Wayfarer Marine or Camden Yacht club. But do it early as its a popular harbor. Or reservations for moorings from the same outfits in outer harbor. Rocky rolly out there though but not too bad.
Castine also has fireworks. Rent a mooring from Eatons Boatyard or space on a float from Dennets Wharf (again, advance reservations recommended). Or anchor in Smith's Cove (quiet anchorage/good holding) a little bit away to the eastward.