You might want to start by studying some charts.

Eastern Long Island Sound, and Western Long Island Sound.

Estimate how much ground you can cover in a day, based
on the speed of your boat, and pick places based on that.

On the western end, the Long Island side is nice. There are
no harbors on the north east shore of Long Island until you get
to the claw.

Most of Connecticut is beautiful. Fishers Island Sound is gorgeous.

wrote

Re. a mini-cruiser single-handing sailing to/fm City Isld & Block
Island in mid-Sept. who wants reasonably long days traveling on the
water but would prefer a marina slip or at least a moorting rather
than anchoring, what's the "best" routes to/from in terms of
sights/accomodations?

If it becomes feasible to expand the trip to/fm Block Island, where's
the "best" place to go before returning to City Isld?