50k miles shouldn't be too hard. I've seen a lot of bikes that are maintained well and make it up to 75k and still going.....there's people with way over that as well. A bike probably won't be like most cars where you can do 100k miles with only changing the oil...you might have to do some small stuff here and there. If you take your time it still shouldn't be too hard find a bike of those years with lower mileage than 25k to start off with.

ergos...all depends on the bike and how they fit you. They feel different from year to year so you'd have to sit on a ton of bikes. Might want to look at the fz1 vs r1 or fz6 vs r6 and so on if comfort is really important to you. Maybe check out the vfr's or some other sport touring bikes. You can get bar risers and peg lowering brackets for a lot of bikes which would help out a lot.