We've visited friends who live near Webb Cove on Deer Isle and it is a good jumping off spot. Three on a 19'boat sounds tight for overnights, but there are a number of spots within a long day's range, or you can try overnighting if it's OK with Bill. First to mind is Woodenboat, in Brooklin. It's essentially due north from Webb Cove at the eastern end of Eggemoggin Reach. It will take you about two hours to get there, (I think it took us one; Eclipse is pretty quick) and we spent several hours there and sailed back the same day. Just west of Woodenboat (maybe two miles?) is Brooklin itself, where there's a small, friendly yacht club, a general store, and a library with original illustrations from E.B. White's stories. Further up the Reach is Buck's Harbor, which also has a small, friendly yacht club, a good restaurant (when we were there last) and the general store where Sal (of Blueberries for Sal fame) went to get her ice cream. It may still be the same cooler. For less populated venues, the islands of Merchant's Row and others offer private coves with pine-capped granite surrounds to anchor in just minutes off the main channel. Joining the Maine Island Trail Association (MITA:
Maine Island Trail Association | For the protection and enjoyment of the wild islands of Maine.) allows you to go in to shore on many islands and hike or explore. Also check what may be going on in Stonington- Deer Isle's main town, which is only a few miles (by sea) from Webb Cove.
Since you say you want to head down the Deer Island Thorofare it sounds like you may want to explore the western shore of Penobscot Bay:Rockland, Camden, and the like. In a 19' boat that will be a bit of a hike, though in good weather it should be possible. Check with Bill first. Northport might be a good destination for the first day. There is a really neat inlet on Vinalhaven just opposite Northport if you have time to explore. Then you can cross the main part of the bay the next day and pick your destination by the wind direction. Rockland is a city, and has an excellent art museum. Rockport is small and cute, and Camden is crammed with tourists, but is picturesque.
Eat some lobster while you're there, and watch out for the lobster pots!