Hiya,
All I can say is that if you go to OBA then good luck. I went there to do my IMC and Night ratings a couple of years back and from what I hear they haven't changed much since then. Granted I did get my course completed successfully, but more by my hard work than their help I think. I'm not going to run them down or give bad press, but I do honestly believe you can find much better schools for no real difference in cost out in the states.
I am now doing my Multi IR and am doing most of that out in the States. The school I am at here is fantastic, a complete contrast to the last one I went to! The instructors are very good and you are always very well looked after, both during and out of "office hours".
If you'd like to know more about them feel free to get in touch. As for Visas, they are only required if you are doing professional flight training, so for a PPL all you need is an I-94 visa waiver the same as when you come here on holiday as it is recreational flying (as long as you don't intend to stay longer than 90 days of course!).
All the best with your future training.