Many of us are in the same "boat". IE: We will be looking at 15 to 25 year old boats.
Yes you need a survey.
Yes you need to become as well educated as possible.
In my opinion their are two major classes of boats.
Class 1
In the first class you have a boat that was bought new by a knowledgeable owner with the money to do it right.
Everything on the boat is on a rigorous maintenance and/or replacement schedule.
Barrier coat, bottom paint, Sails, running rigging, standing rigging, bedding of all deck fittings, chain plates, tangs, tanks, engine, through-hulls, hoses, electronics, wire, paint, pumps etc.
This owner will have a log with everything done on the boat along with receipts and part numbers. You will find that just about everything has been replaced at least once maybe twice in 20 years.
Once you buy this boat you will find that as obsessive as the PO was he will have forgotten something that you will have to then dig into for the first time in xx years. But yes you will have a pretty good boat.
Class 2
The boat was bought and repaired as things broke. When you buy this boat it is entirely possible that you will be able to continue to fix things as they break for many years and it not cost you too much.
It is also possible that you will hit one of the big unexpected ones. Things like soft core, hull to deck leaks, engine problems are some of the things that many not show up on the survey.
The bottom line is that their is a lot of luck involved. We don't like to talk about it as it is uncomfortable but it is true. Some really competent smart people get hit with big repair bills and some total noobs get away with everything for years.
But of course percentage wise clueless noobs get taken to the cleaners most often but anyone can be unlucky.
Class 1 boats sell for the top price of their class usually to people the OP knows, often very quickly. They account for less than 1% of the market.
Class 2 boats are a what most of us end up with and we have to take our chances.
The other alternative is to buy a Class 2 boat and do a full refit. It takes from 50% to 100% of the purchase price and about two years for most people. Then you have a class 1 boat for a couple years until you get behind on maintenance.