-- Last Updated: Jun-17-12 5:57 PM EST --
You will likely get various suggestions on models to look at. We all have our favorites so I will pitch mine - I am about your size and have owned 8 touring kayaks (as well as borrowing or renting several other models over the past decade). If you have a chance to test one out, the Venture Easky 15LV (made by P & H) is a reasonably priced, well outfitted and nicely performing plastic kayak for the kind of paddling you are describing. At 44 lbs it is lighter than similar boats in the 15' range and it is designed (low volume) for people of moderate weight and height. Actually, it is very much like a sleeker version of your Castine, a few inches narrower and 2 feet longer, with two hatches (of course).
Mine does not have the rudder but has all the mounting and cabling channels to easily install it -- frankly I have never felt it needed one. It tracks and accelerates very well and handles solidly in waves, wind and rough water. Very comfortable seats, thigh hooks and foot pegs. I've loaned it to friends who were at the stage of stepping up from a beginner boat and they have all been very happy with the feel of it. The Easkys are attractive boats too (mine is bright spring green, now tagged "The Snow Pea"), made in Great Britain.
You mention New England -- if you are ever near Lake George in upstate New York, Lake George Kayaking outfitters has them in their rental livery and they were selling some of the rental models for several hundred off the list price (new price is around $1100.)