You raise a number of interesting questions, but I also think you may need to think a bit more about what you want to do with the boat.
As a start, are you planning on sailing with just you and your husband, or do you have kids? Do you plan on overnight guests, or will it be just the two of you sleeping on the boat? If it's just the two of you, then I would think the 393 would be fine for size and might save you a few bucks. If you will be sleeping more, however, then I would strongly recommend going with the 423. Another consideration is sailing ability. The 423 will sail MUCH better than the 393. Just another thought.
In terms of costs, sailboats do cost less than powerboats to maintain. Obviously fuel is less expensive, but it seems as though they are less expensive in other ways. That said, maintaining sailboats is not cheap. If you do the work yourselves, you can reduce the maintenance costs dramatically. Unfortunately, there is no real way, in my opinion, to determine in advance how much it will cost to maintain a boat in the abstract. If you tell me what will break, what upgrades you want, and what work you will do yourself, then I can give you a better understanding of what the costs will be. Obviously you can't do that in advance, which is why it's very difficult to predict. I will say that $1,000 per year seems low, unless you will do ALL the work yourself (including commissioning and decommissioning). Just to pull a number out of thin air, and assuming you do at least some of the routine maintenance (oil changes, some decommissioning, etc.), I would say that $3,000 to $5,000 is probably are more realistic number.
On the bow thruster, you certainly can get by without it. You might have a few exciting moments your first few times docking, but you would learn to live without it. That said, if the money is not an issue, you will like having the thruster. Even if you choose not to use it all that often, when you need it, you will find it invaluable.
In terms of a place to keep the boat, there is nothing wrong with New London in terms of its proximity to other places, but it's not the nicest place. I would consider some of the places on the Mystic River, south of the bridges. Or maybe somwhere on the Conn. River. Westbrook also is nice, and there's a great Brewer's there (Pilot's Point). Again, nothing "wrong" with New London, and it is a convenient to Block, Shelter Island, etc., but there are nicer harbors in that area that also are convenient to these points of attraction. Just my opinion.
One other thing about Block. You might find that taking a mooring is preferable. This is entirely personal preference, but the moorings there are very close to shore, you easily can dink in, or even take the launch. Yet, when you're on the boat, you have more privacy on the mooring, it is more quiet, and more pleasant, IMO. But if you really feel you NEED to be dockside, I'd go with the Boat Basin over Champlains to avoid having other boats rafted. The last thing I want when staying on the boat is having numerous strangers climbing over my decks to get to/from their boat, and many of them are a little light on etiquette, so they go through the cockpit, look in the hatches, and stuff like that.
Good luck!
