We did same cruise on NCL Dawn last October. Do take a coat as although it was warm in NY it was quite cool on deck.We did our own tours not Ncl which was great. There is a free local shuttle bus in Bar Harbour which takes you into the Acadia Park, and you must eat Lobster at Testas. Newport get the tram/trolley for a few dollars and do the mansions yourselves, Marble house lovely. Then you must go to Brick Alley Pub for mega Bloody Marys and burgers.Have fun, we did, freestyle was great!
We sailed in the reverse direction 2 years ago. It was chilly in the Canadian ports, Halifax etc and it snowed in Boston but I think this was unusual. We had weatherproof hackets and used them for this leg of the cruise. From Boston down however it was warm enough for light trousers, t shirts on shore ex with a light jacket, just in case. You will probably need a woollen of some sort for sea days. Might be worth looking at a long range weather forecast just before you go. Try www.worldweather.wmo.in.