There are a few good harbors near you to consider. I keep my boat in Essex Bay so we have roughly the same overnight cruising grounds.
Rockport: This is the closest but also the most crowded if you want to go into the inner harbor. There is always plenty of room to anchor out off the town beach (you may be anchored in 40' at low water) but call the harbormaster ahead of time if you want to get into the inner harbor. Be aware that you should not be anchored there with a large ground swell of heavy winds from the north or east. Sailing time there will be only a few hours if there is decent wind. It is not unreasonable to sail there and back on a nice day.
Gloucester harbor: This isn't quite as pretty as Rockport in my opinion but is sheltered in almost all weather. The harbormaster maintains several moorings and there is a good anchorage in the southeast harbor. This is a reasonable length sail in most weather. If you find yourself becalmed, you can shorten the motor by taking the annisquam canal, just be careful not to be going against a strong current on the Gloucester harbor end.
Portsmouth, NH: This is another good destination and there is always room to anchor in Portsmouth harbor at the west end of the mooring field. It can be a long beat home with the prevailing southerly so watch the forecast.
Salem sound: There are many anchorages or places to pick up a mooring here. It will probably be farther away than you want to try for your first overnight but is definitely a reasonable destination for you once you become comfortable with the area. Many of the anchorages can be rolly in the right conditions.
I hope that this helps. If you figure that you can average something like 3 knots, you can get a pretty good idea of your cruising area for an overnight.