1. The terms might preclude you using it as a UK resident but they are not enforced or in any way enforceable as MP Dining doesn’t ask for any relevant information. I’m a UK resident (and always have been) and have used MP Dining for years.
2. It works off credit card numbers. You register your credit card(s) with them and the transaction posts automatically. I have three US cards registered with them but no foreign cards. I don’t know if it would work with foreign cards.
3. Don’t think so but not sure.