What exactly do you mean by "Early 2017"? Many campgrounds in New England don't open until maybe late May or early June or so.
If it's early enough, biking will be very adventuresome (and cold), hiking pretty adventuresome (and cold), and fishing mostly consist of huddling down and watching for a little flag to flip up (and, yes, also cold).
Bar Harbor area is probably about as reasonable a central-ish area as any. Acadia is a beautiful park. The Maine coast is fairly long, though, so moving about might be more practical than trying to have one single home base.