Don't worry about 650's, I've been riding them for 12 years and I have no problems getting wheels, tires, tubes etc. Last year I had a custom frame built for 650's and had handbuilt wheels (custom) made for it. No issues with getting the rims. I use a 23c width tire which is pretty common.

Performance often puts tubes and tires on sale.

My biggest issue is when my SO starts to climb I run into him because he doesn't accelerate as fast as I do due to weight and wheel size.

I run 85 psi in mine, recommended by the tire manufacturer for my weight and they give me a nice smooth ride.

I get no more flats than anyone else gets or what I get on my mtn bike. As long as I stay away from the goat heads around here I'm pretty flat free!

I do carry 2 tubes with me because other riders don't have tubes I can borrow.