£800, I know you can get for £999 new, but it has a lot of upgrades. Specced it New on the PX web just now and it would be £1700 new. Its not done 100 miles.
I'm 6ft dead and its fine for me, think it would still be fine if I was a couple of inches taller. I guess as the above link says, you could go either way. I reckon it depends on what you intend to use it for, If you are building it up light as a XC bike, I'd say 20" if you want to do more gnarly technical stuff on it then I'd say go smaller
So its more of a strength issue rather than cog teeth spacing. It seems to run OK but does rattle a bit against the bash guard. I guess I could space the guard out a bit with some thin washers/shims.