I have a home on Martha's Vineyard and have also fished the flats on Chatham and Monomoy. When the conditions are right, the fishing can be like Bahamas Bonefishing - gin clear water and Stripers over white sand...very cool. Access and crowds are the big problem. Summer on the Cape gets crowded - especially weekends. Mid-week is the best to avoid crowds and traffic.
Having the skiff will give you plenty of options but again, weather dependent and you won't be comfortable fishing any of the big rips where the big girls live. A lot of guys in the NE fish at night and you can have incredible success fishing from shore with flies or artificials. Like most other places, the guides are territorial and don't like sharing spots with folks
"Not from Here".
Some of the Ponds are full of fish but ramps are few and far between and most require a local parking permit in order to launch.
Stripers and Bluefish make up 99% of the fishing but you can also bottom fish for Scup, Blackfish & Flounder. Albies and Bonito arrive late August and stick around till October.
2 great sources for local information are;
On The Water Magazine
https://www.onthewater.com
Salty Cape website
https://saltycape.com