Not who you were replying to, but on mTurk 10,000 approved HITs with a 99% approval rating or higher will probably be your best bet. If you are going to put up a lot of HITs, especially if your HITs require special skills, you might want to put up some tasks and assign a special qual to the top, say 10 or 20% of the workers. Then you'd have a more limited group of workers, but ones that you know will do well. (Usually qualification tasks require workers to complete 10-20 of the HITs to get a good idea of the quality of work.) You might sacrifice a little bit of speed, but you'll get better work. Plus, if your work pays decently by mTurk standards, anyone who has the qualification will be on the lookout for your tasks.

Honestly, I'd get an EIN from the IRS http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employ... For international businesses, it requires a phone call but supposedly it's not terribly difficult. Get a mail forwarding serving so you have a US address for Amazon payments, and from there it's just a matter of sorting out a bank account or US credit card. That might be a bit more difficult, but the easiest thing to do (if a little bit of a grey area) would be to get someone in the States to get a prepaid card like Serve AmEx, Bluebird AmEx, or prepaid Paypal mastercard. All of those cards are prepaid, but they have a routing and account number that could be set up as a bank account on Amazon Payments. The Paypal one would probably be especially handy since it could be funded from a foreign bank account or a PayPal account.