As animeme said, even small Jewish communities often can't even support a single kosher restaurant. Any place with multiple options is by definition going to have a significant Jewish population. Places near NY with multiple kosher options include Boston, Philly, and Baltimore. Waterbury has nothing and even Norfolk I believe only has one shwarma place, so you'll have to choose your priorities. I believe there's a kosher pizza place open twice a week near Scranton, so maybe you could go to the Poconos, and stock up there?
Got it. Houses with pools go fast and are often booked by now for summer, but sometimes you find a metziah. And without a pool is much easier.
Assuming you're not going for Shabbos, I actually still recommend the Long Branch/Deal area, but don't stay in Long Branch or Deal. Find a house in a surrounding town and drive in fifteen or twenty minutes for food and minyan. You can even order takeout and send one person to bring it back to the house. Brielle and Spring Lake are towns that come to mind.
Boston can work too depending on what you can find geographically. We have done the Cape Cod area, renting a house on a creek that was a ten minute drive from the Onset minyan. You can drive an hour into Boston on a day at the beginning, do something in the city, and do takeout from a few places and heat one meal up per night afterwards.