Kris and J,
Check out Boat Search 101 at the top of the "General Discussion" forum.
Take the time to plan out how you envision you are going to use the boat. Short weekend type trips or long trips of several months? Guests often or hardly ever? Open ocean like west coast of Vancouver Island or all protected waters? You get the picture.
Then make separate lists. Must haves, nice to have, and don't want. Then compare lists, discuss, and compromise (a tie goes to the Admiral
). Then talk to other boaters asking lots of questions about what they like about their boats, things they would do differently, etc. There could be some useful info there. Walk the docks, go to boat shows, and view lots of boats. Once you have it narrowed down, considering your budget as well, then you can focus in on a few brands/models that check off most of your "boxes". Boats are a compromise, so it would be rare to find one that is "perfect".
Being as I already know your outlook is that you want to enjoy your boat, not work on a project, past maintenance and care is critical to get a boat you will be happy with. It may take a bit of time, so be patient, but they are out there. Also plan on spending a fairly large amount of money after purchase repairing things, upgrading things, and adding things. In other words, don't max out the budget to purchase.
Most of the things you asked about are mostly "personal preferences" and there are no right or wrong answers. Things like twins vs single, brands of engines, generators, appliances, etc. I will address the engine hour question. Another NT 37 owner has over 10,000 hours on his 2000 Cummins 6BTA engine and it is running great and he will probably get many more hours from it. He does maintain it very well!
Maintenance is critical and how it was run is critical for long life before a rebuild is required. However, be aware that very low hours (for an older engine) can be worse than higher hours. Diesels don't like to sit for long periods of no use. As a ballpark guess, I would say much less than 100 hours per year of age could be a sign of potential problems for lack of use. However there is no hard and fast rule.
I will give some of my "personal preference", but they may not "fit" into what you want in a boat, or may not be "your perferences", and that is just fine. That is why they make so many different makes, models, and styles of boats.
I prefer single engine (many others differ). Twins cost more to maintain and repair, and in the boats I viewed in the size range we wanted (could afford) with twins the engine room was too cramped to allow access for maintenance. I have a Cummins 6BTA engine and they have a very good reputation. We have a Onan generator in a sound shield with a split exhaust. Very quiet. Northern Lights make a good unit. Solar is a very good idea to allow full recharges if you like to anchor out a lot, potentially increasing battery life. I prefer propane stove/oven to electric. I don't want to have to run the generator to cook or boil a kettle. We had only a few items on our "don't want list". Screwed down teak decks, exterior brightwork, and a flybridge. Again, there are many who have different preferences. You need to determine yours.
It seems like a daunting task, but take it a step at a time, take your time, and be patient and you will get there. Good luck.