One thing I did miss! I don't recall any form of statutory MOT or test (at all). I just took my motor in for oil/filter etc changes every couple of thousand miles, but that was completely at my own discretion.
And I can't see a UK company issuing motor insurance on a car bought in America. I expect you would have to get it in the US. (I used to insure via
http://www.statefarm.com/insurance/insurance.a sp
if you want to look into this aspect some more.)
Thinking about it more. Perhaps you might consider that unless you have a base (friend/relative) in the US, buying your own car for a one off trip might be pushing your luck. Otherwise I mean, if you wanted to eventually sell your car, what are you going to do, sit in a hotel room for a week, two, longer, while you try to sell it?
If you're only planning on going for a few weeks, I'd suggest that hiring a car might be a hell of a lot easier, and less stress. If you're going for longer, to work/live/study perhaps, I'd say go for it, but allow plenty of time...
Have fun!