Lots of points to answer for what seems a very simple question. I'll try to get through everything!
First of all - hour building before the exams. Your logic is good, but not perfect. Someone else has already mentioned that a bit of flying on the side might help relieve the pressures of the studying, which is true enough. More importantly, though, you don't want to go into your CPL training having not flown for 6 months or longer - you'll end up spending a few hours getting up to speed. I'd suggest doing half, maybe three quarters, of your hour-building first, and leaving a few hours until after (or during) the exams, so that when you turn up at your CPL school you are current.
Next question - where to go. USA is good. As Strafer says, you don't actually need a Visa to hour-build there. Strafer knows that, I know that, and now you know that too - but none of us matter. The only person who matters is the immigration oficer who happens to be working the day you turn up. So, although it's not required, it doesn't harm to get a Visa anyway if the USA is where you're going, because the immigration oficer most like isn't a pilot, and doesn't understand the different between training and hour-building. Most likely you'll be ok, there's a small chance you won't be.
As to where in the USA, I flew out of Chandler Airport in Phoenix, Arizona for two months, renting from
Chandler Air Service - I'd definitely recommend them, and I'd definitely recommend the area.
However, with hindsight, I would not have done my hour-building in the US. I'm planning on going to the US for my CPL (I say planning, it's already booked so I guess that's more than just planning). With one exception, every CPL school outside of Europe is in the US - there's a reasonable chance that you'll go there at some point during your training anyway. So I'd suggest going to somewhere more unusual for your hour-building, just for the variety. Canada is beautiful, although I've never flown there. I've heard good things about South Africa, too, but never even been there. If I had to do it again, I'd have chosen one of those places to go for hour-building, and saved the US until I did my CPL.
Hope that helps. But wherever you go, remember that hour-building is there to be enjoyed - make sure you learn and improve, but have fun while you're at it!
FFF
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