The USA is a good idea for the following reasons;
The cost of flying out here is a lot less than the UK or Europe in general. Become a CFI and gain many hours of flight experience in a short period of time. I taught at a JAA (CAA) school where I would fly 6-8 hours a day.
The USA is going through a pilot shortage. There are many companies out here that even if they hire as many pilot's as they can this year they will still be short!
You can gain the multi crew experience by flying for an airline in the USA whilst completing your ATPL's, you can even take the exams out here now (Orlando).