David and Emma,
Welcome to Sailnet!
I would recommend the Herrington Harbor - North
marina for your purposes.
It is a large yard, upper-mid-Bay, on the Western shore of the Chesapeake, about 15-20 miles south of Annapolis. It is within striking distance of two international airports (Baltimore-Washington International, and Washington-Dulles International).
They allow DIY work there. Also, they have (on-site) numerous marine services for rigging, structural, sail work, etc.
And there is West Marine chandlery at the marina.
Good luck to you!