Your question about "high miles" is a tough one to answer simply. I've seen bikes with 10,000 miles on them that are pretty much toast. On the other hand there are bikes with 30,000 miles on them that have been well cared for and would easily do another 30,000.
You just have to use all your senses when you check out a bike. If you aren't real confident about judging some of the tricky parts like engines and transmissions, hire a mechanic to help you. The $100 fee they usually charge is well worth it in the long run.
I've got 3 bikes right now, two have about 10,000 miles on them and one has 20,000. Guess which one is in the best shape? Yep, the one with 20,000. If you look at a bike that has more than 40,000 miles on it, look at it very, very carefully.
Finally, after many years of riding, I would not get a large bike unless it was for a VERY long trip. I find smaller bikes are much more fun, easier to handle and move around.
My favorite bike is a 1977 Honda 400F and I wouldn't trade it for anything. ANYTHING.