Time to do lots of homework on purchase

I would restate that as "be aware of any production built older models that have coring material below the waterline". Very few of the production manufacturers have had success with this approach, and it certainly can be made worse when less than capable yards making equipment installations in cored bottoms - Sea Ray and Hatteras felt this pain big time (as well as a host of others).

Having lived aboard my boat (65ft.) for about 2 years now I´d suggest to think about buying a little bigger. You´ll be surprised how much unnessesary stuff you carry through your life. But even though moving on a boat is a good reason to sort these things out you´ll still find lots of things you don´t want to dump or sell.

Besides that I don´t think that negative about old hats. An old slightly bigger Hatteras offers plenty of of space and gives you the possibility to rebuild some of that to fit your needs.
You could install a small office, have a reasonable guest cabin and some extra storage.

Only important thing is a good engine condition since problems down there can be pretty expensive.

The rest depends on your skills, creativity and the decision if you´re willing to do some work by yourself. (but that´s just the opinion of a geek who built his own boat)

Well, in that case a boat that fits your requirements the way it is would obviously be the better choice.

1. as a very (very) rough rule of thumb, $1,000 per foot of boat is a workable number for an excel sheet. This is highly subjective based on use, boat, vintage, etc. but if you were to pencil in $1,000 per foot, you'll be close for budgetary forecasting.

2. Yes, but no. It will be a challenge to find someone to rent it, care for it, use it, etc. It opens a huge can of worms that if and as I'm reading your thread, this is a first (larger) boat for you, so things to take into consideration are insurance, maintenance, break and fix, docking, taking it out without you, captain, etc. Again, having a renter on your boat as a liveaboard is right in line with pandora's box. If you run into issues, your backup plan is to sell it in a fire sale.

Ditto on what Propbet said. If you own a boat and run into financial problems, expect to lose a lot of money, and the problem may linger as many found out when the markets crashed in '08 as well as in the early 90's. Forget subletting. It just won't happen which is a good thing because the Pandora's box that Propbet referred to is big, nasty and expensive. All you need is for the renter to trip or cause a fuel spill and you'll be living with your lawyers.
Another rule of thumb for estimating maintenance costs on a boat is 10% of the new boat purchase price.
One thing that caught my attention was bottom painting every 3 to 5 years. I'm not personally familiar with your waters, but here on the northeast coast you'd have a barnacle farm. Down in Florida it'd be 6" thick. I think you should figure every 2 years at most or plan to have a diver down very often during the warmer seasons. Forget sanding yourself. Most yards today won't let you touch bottom paint without an environmental license (pesticides). Zincs are changed annually. Their a soft metal that sacrifices itself so that electroysis doesn't eat the important metal in your boat, like the through-hulls for your motors and a/c. That would leave you on the bottom. You'll generally find zincs attached to your shafts, trim tabs and possibly to the hull, as well as in your engines.
Living on board is one of those things that for most is better in theory than practice, and seldom for a couple.

I have rarely seen zincs go annually, especially if you're living on the boat and using a lot of electricity. Here in FL, I am usually getting 3 months-6 months out of zincs on most boats. But living aboard, I usually see people go through them every 2 months since you're using so many electrical items on the boat.

You can throw that 10% rule out the window in this market. Many brokerage boats that had a market value of $400K five years ago are selling for $200k today but the cost of maintaining the boat hasn't dropped by half along with it's purchase price. While your boat buying dollar may go farther today - your boat owning dollar does not. Fuel, parts, slip fees, taxes, insurance, electronics and equipment, haulouts, labor rates, etc are not in any way connected to a boat's continuing loss of market value.

A 54' Bertram that you can buy for $175K today will cost as much or more to own and maintain as it did back when it cost $500K - you can do the math.

Another rule of thumb for estimating maintenance costs on a boat is 10% of the new boat purchase price. IOWs you may have paid 100K for a boat that originally cost $1M, but you should still expect maintenance costs of roughly 100K annually, and more if you use it or maintain it well or if you happen to buy it the year a motor decides to die.

Who is buying a new boat in this thread?

Recreational boating typically does not have a financial upside. The best situation you can consider is to enter it from a lifestyle perspective, preferably the most major part of your lifestyle besides your land base. This way you can create life experiences for your family that would be difficult to put a price tag on

Depending on how many hours you run, fuel will be the biggest variable expense. It is to hard to determine what mechanical repairs you may face, that is why you want the most stringent engine/transmission/generator/vessel survey done prior to purchase.

As far as the engines/transmissions/generator go, talk to the area servicing distributor and get estimates of scheduled and non-scheduled maintenance costs, up to an including overhaul to determine your worse case scenario.

In SoCal, we have divers scrub the bottom growth and inspect the running gear every month, not a big deal, and should run under $100/month. Bottom paint can last from 2 - 5 years, get quotes from your area boat yard, they will typically give you a $/ft approach.

Fire sale scenario - really difficult to predict actual values, there are some broker/wholesalers out there, but in today's (and the next five years) market the ROI is way down and would probably shock you and/or your wife

RER, are you intentionally trying not to understand what was written? Let me spell it out slowly. If you buy a $1M boat the anticipated maintenance costs are about 100K annually. If you later sell that boat for $0.50 the anticipated maintenance costs for the new owner will remain about 100K annually, despite him only paying $0.50.

Got it CAP... not in your first post, but in your second post - I do smell what you're cookin' ...