Re: Best week to sail in MA
We sailed a Cal 33 "Cheap Sunglasses" out of Westport the week after Labor Day this year. The launch service at Tripp's had started closing at 3 pm on weekdays after Labor day, so call them to make sure you can get to the boat!
Otherwise I agree that it very pleasant to sail around New England after the Summer is over. The Newport Boat Show was also the second week of September. If you wanted to either engage with crowds you could go to Newport then, or miss them by going the week before or after.
We went to Manemsha and Cuttyhunk. The weather was OK for New England (some rain) and the water was warm enough for swimming.
We got a ride on the C.W. Hood 32 at the Boat Show (very nice!) but had to rush back to Westport because of the launch hours. The people at Tripps were very nice though. Just beware of possible reduced launch hours after Labor Day, so plan on a slip or using a dinghy more in the Fall perhaps.
There are far fewer crowds and generally as nice weather as anytime in the Summer in September (and October).