Having spent many years on the Connecticut, I can only tell you that it is a beautiful place to cruise. Consider it in three sections: Old Saybrook to Haddam; Haddam to Middletown and Middletown to Hartford. There is almost always a lot of boating traffic in the lower river but there are many marinas for fuel or transient dockage there. If you want to stop in Old Saybrook on arrival, pull up to a gas dock on either side and ask about accommodations. Old Saybrook is a nice small town but quite a long walk from the marinas. The next town up river is Essex and it is certainly a worthwhile stop, although not much of a "resort" for kids. Brewers has two marinas there and Essex Island Marina is a favorite for many visitors. The Griswold Inn in Essex is wonderful.
If you want to go further - and I would - go up as far as Haddam, where there is a swing bridge with better than 15-16 feet of clearance at very high tide. There are marinas in the Haddam area (Hay Haven in Chester and Midway in Haddam are two I can think of). Again, these are small marinas in small towns but that's what many boaters are looking for.
Most visitors don't venture north of Haddam but the river is easy to navigate and plainly marked. The next fuel and transient stops are in Portland, across from Middletown, 33 miles up from the mouth of the river. Yankee Boat Yard has gasoline and takes transients. There is no diesel in the upper river. From Portland you can get a ride across the river to Middletown which has many nice restaurants and a main street that looks like the 1940s. You can also usually tie up at the Middletown municipal dock (no water or electric) but put of lots of fenders.
It is rare to see visitors head up north from Middletown, although the river is easy to navigate and passes through some beautiful Connecticut countryside. There are no marinas in this final stretch of the navigable river and at the end, Hartford has a beautiful skyline but no real place to tie up.
At that point, you'd be about 60 miles from Old Saybrook.
I don't know of any marina on the Connecticut that I would classify as a "resort," although some of them have pools. The best part of the river (especially on weekdays) is that you can slow down and enjoy yourself. There are eagles nesting above Haddam now and in deep summer, it is just a beautiful place to enjoy being on the water.
For help once you are in the river, just put out a call on Channel 16 for "local info on the CT River" and you'll get plenty of information.