I've done part of the ACA atlantic coast set. I have the two sets that takes you from NYC/NJ/PA up to Bar Harbor but since I live in NJ and have done my own routes near me, I used only a small section from New Paltz to Millterton, NY, the rest I simply using my own knowledge and local street maps. I did a ride from my house to the Berkshires last year. I do know that there are some camping in CT and probably even more than those that are listed on the back of the ACA maps. Find a decent city and use Google to see if you can find camping destinations. Otherwise, there is always stealth camping.
As far as the traffic, road conditions, etc, going east and west through Dutchess/Putnam county consists of rolling hills east of the hudson. Kind of a pain to keep going down and up and down, but it is pretty much free of traffic once you get out of Rt 9 through Poughkeepsie, Hyde Park, etc. You will have lots of traffic over the Mid-Hudson brige and up Rt 9. Once you get past the Vanderbilt Manor though, it gets more scenic and less traffic. The Manor itself is a good spot for lunch (right on the Hudson, go down to Bard Rocks and there are some nice picnic tables you can eat at. Free too, unless you go into the Manor itself).
Anyway, after the rolling hills, it does level out once you get towards Millterton and into NW CT. I've gone to Salisbury CT on the way home, but when my friend and I rode to the Berkshires, we headed north on Millerton to Bash Bish Falls and then east on Rt 23 to Great Barrington where we basecamped. But on the way back we took a route parallel to Rt 7 by some covered bridges to Salisbury and then west. Nice ride!
I would say most of that route will be rural except for the Poughkeepsie area where you cross the hudson. I have never done the section through Providence or Norristown so I can't speak for those sections. Obviously the closer you are to Philadelphia, the less rural you get but I think it isn't bad cause you're not really going into Philly.
There is also Harlem Valley RT in Millerton that goes to Amenia, which I wanted to do, so I did this as an alternative to following the same route back. If you do decide to do this, pick up a dutchess cty map and you can see Rt 40(?, I think!) that goes from Amenia towards Poughkeepsie which is your destination across Dutchess Cty. Be Aware that there is a HUGE ASS HILL(tm) just outside of Amenia that you will have to grind up. I did it with a FULL set of panniers and very loaded but I had a MTB with MTB gearing and managed OK. My friend was suffering on a road bike and only 2 panniers. It's doable but it is tough cause there is traffic on that road, a small narrow shoulder. However, there is a great view at the top of that hill though.
Feel free to ask me anything else that I may help you with. I'll try my best.