Another things to consider on wells is the hardness of the water. Even if you like the taste of hard water, you need to consider how much mineral content is flowing into your water system. I had a water heater reduced to about 1/3 capacity because the previous owners both removed the filtering and failed to flush the hot water tank. The bottom of the tank filled up with calcium and actually destroyed the lower heating element.
I do not have an informed opinion choosing between filtration or water softeners, but you need to be sure you have one of them if your water has any serious mineral content. (And if you go with filtration but skimp on changing the filters, be sure to flush out your water heater a few times a year.)
Pumps come in two varieties: 1) above-ground pumps that any ten-thumbed, mechanically challenged shlub can replace (Speaking!); 2) in-ground or submersible pumps that are placed on the end of the well’s service pipe and pushed or dropped (gently) to the bottom of the well and generally need some expertise to install.
The above-ground pumps only work to a certain depth, below which submersibles are required. The above-ground pumps are a lot cheaper–and they last a lot longer, but if your well is too deep (or you really need the higher pressure), then you need to go with the submersibles. (Submersibles also require (I believe) a 4 inch pipe, while above-ground units can get away with 2 inch (or even 1 inch) services.)
If you are buying and not building, ask when the pump was last serviced. The above-ground pumps can go 20 years or more with no service at all, I have never heard of a submersible lasting eight years. (They may last 40, but I have never encountered one that got to 10.)
Look at the pressure tank. If it has a little clam-shaped device on the outside with a separate thin water line going back to the pump, it is ancient. The clam-shaped device has a diaphragm inside that is used to let the pump know when the tank is filled. Periodically, the diaphragm tears (wears out) and needs to be replaced. Replacing it is merely a matter of undoing some screws and getting a bit wet, but finding the blasted part can be a real adventure. (The box my last repair kit came in says OLEN MANUFACTURING CO. 141 ONTARIO ST, FRANKFORT ILLINOIS, RAC-33-3A Repair Kit but I can’t find the part number or the company name on the internet.)
Many houses have been built over the wells. (It makes servicing the plumbing in mid-winter much easier.) However, it is difficult to drive a well-drilling rig into the basement, so replacement wells are pretty much always outside with a pipe running through the wall into the basement. Many wells last virtually forever, but in some soil types the input clogs with grit and a new well must be drilled. This is really hit-or-miss, however. I have a neighbor about 400 feet from me who has had three wells drilled in 15 years. No one else on either street in the subdivision has had a single well replacement of which I am aware.
If some of this sounds scary, it certainly can be. However, my Mom has been in her (47 year old) house for 34 years with only one well and pump replacement and I have been in my (44 year old) house for 16 years and have only had to replace the pump and pressure tank two years ago.