Everywhere is high speed and wifi in this area, it shouldn't be difficult to find a convenient modem to plug into though.

There are a few motels/hotels and B&Bs(email them for access details) within walking distance of the dinghy dock. You can work in the Camden library(all day long, lots of space, work tables), coffee shops(others are working on laptops), your room, probably could even plug an ethernet cable into the harbormasters modem.

Showers at Wayfarer, full service grocery store right in the harbor, all easy walking distance.

The best deal if you arrange in advance, are the inner harbor floats(40/45? night, showers, laundry, free pump out boat, wifi to the boat). Very protected(unlike the outer harbor), very short row or cheap long hours water taxi to the dinghy docks, private yet in the center.

This may be a good place to start and then move onto other areas of interest.