+1 - September is a great time to visit the Northeast. In October, during the fall foliage, you'd have a hard time finding accommodations. But you should be fine in early September. My "destination" in Maine would be Mount Desert Island, aka Acadia National Park, aka Bar Harbor. There is nothing much worth seeing north of that, and that area is among the prettiest places on earth.
As for motorcycle roads, other than the roads on Mt Desert Island itself, there really aren't many "twisties" per se. The mountain states of New Hampshire and Vermont have more of those roads. Maine has the scenic coastline.
As for getting there (and back), my advice would be to stay west of the coastline until you get north of Boston. We live ~45 minutes from the coast here in southern NH and whenever we head down south (for EOM, etc.) we always start out by going westward through the Berkshires in Mass, and the Catskills in NY to avoid the I-95 corridor congestion of Boston, Providence, Connecticut, NY City, and New Jersey and Philly. None of that is a fun ride.
Here's a rough idea of a route I'd take. I've routed the northern portions and just let GoogleMaps find the southern parts. You probably know those parts better than me. Using GoogleMaps to plan routes is easy. Just click on "Show Options" and "Avoid Highways" and it will take you up some nice state roads. By the way, we typically take 3-4 days to make that trek. 2-3 days if you resort to the slab.