Cape Cod has great beaches the further you go towards Provincetown. There are lots of shops, lots of scenic spots, and quite often.. Lots of traffic!
If you are heading north of Boston and are looking for lighthouses, you might consider Portland, Maine. There is a narated harbor tour that takes you to see 7 lighthouses (weather permitting)..Portland discovery Land and Sea Tours. They also run trolley tours of the historic city sights and take you to the famous Portland Head Lighthouse where you can walk around it! There are over 100 restuarants of all sorts in Portland. It's a very nice city. The fall foliage comes later at the coast than it does inland..so you might want to check inland first on your trip!
Congrats and enjoy New England!