Re: Used equipment
It is difficult to give solid advice on such a broad question. A lot will depend on what you intend to do with your boat - a weekend warrior is very different from somebody doing offshore cruising. A boat sailed in saltwater ages faster than one sailed in freshwater.
Another variable is how often, and how hard, the target boat has been sailed. I have done more sailing on my boat that the PO had done by a ratio of 3:1+. And my sails, running rigging, etc, are aging faster! Racing boats tend to be used harder than fairweather cruisers.
Having said that, electronics become outdated before they fail. My GPS is almost 10 years old; it is in black and white, but works fine for what I want. My knotmeter and depthsounder are original (30 years).
Some *major* ballparks: Standing rigging - 10-15 years. Sails - 10 years, longer if you don't worry too much about performance. Chainplates - 25years. Engine - depends heavily on maintenance.
Best advice I can give - look on a new boat as a collection of parts. Unless you have a lot of money, you probably won't be able to buy many more parts (look at me and the old GPS). A well-equipped older boat may well be a better deal than a sparely-equipped newer boat. My boat only came with 3 sails (main+ 2 headsails). A buddy bought a slightly smaller boat with 6 sails (2 spin, 3 head, main). I am kinda jealous about his sails...so when you look at boats, look at what they have, look at what they need, add 10%-20%, and there will be the true price.
Final thought - see if you can get some advice (definitely use a qualified surveyor). Don't fall into to the common mistake of buying a boat for (say) $15k, investing $20K, and ending up with a boat worth....wait for it....$15K. That's why I say look at the boat as a collection of parts. Most stuff you buy for a boat (especially electronics) is generally worth $0 when you install it. Much of the stuff you are talking about does not (should not) add materially to the value of the boat - despite what sellers may think. The stuff just helps you choose one similar boat over another.