Sag Harbor-NYC-Atlantic City
To do this trip without knocking yourselves out, make sure you''ve got the tide with you - especially through Plum Gut. From Sag Harbor in a day you can likely make Saybrook, CT, or possibly Port Jefferson on Long Island, depending upon the conditions.
The next day - leaving early, and again keeping the tide in mind - Stamford, Norwalk or Greenwich could be targets in CT. Northport, Cold Srpring, or Oyster Bay on the Long Island shore. Manhasset Bay might be a stretch, but that or City Island would put you closer to the city, where timing your arrival with the tide will be all important. Getting through Hell Gate and the East River means waiting for the tide to be slack and then favorable for you. You do not want to be fighting the tide in the East River with strings of barges riding with it zipping past you on both sides going the other way. Going with the tide at least allows you the time to see the other traffic and avoid it. For specific marinas & anchorages on Long Island Sound, the Embassy Guides have pretty good info. Someone else will have to add their $.02 for beyond Manhattan. Happy new boat!