South Berwick's layout is very much like the early maps. It is a nice village with many old homes, civil war monument, etc. The Congregational Church is in the middle of town where it was built in the 19th cent (the old meetinghouse was further outside of town.). There are old mill buildings (19th cent?) on the outskirts and 18th and 19th cent houses in the town center. Berwick Academy is still active. There are two famous houses, the Sarah Orne Jewett House (right in town, home of the author) and Hamilton House (on the outskirts...a triumph of colonial revival style). South Berwick traffic is amazingly bad for a small town.
The Old Berwick Historical Society is excellent with a small but interesting museum. THey have a good webpage at http://www.obhs.net/
I spent two weeks last summer helping on the Chadbourne House archaeology project. Met LOTS of people with extensive knowledge of the area.
As for the Warren cemetery, Maine Old Cemetery Association lists three small plots. I have not visited any, but from the description of the plots, they sound pretty isolated. You would have to hunt for them.
Hope this helps.