To answer your questions:
1. No, a friend/cohort member received his MPhil from Cambridge. He's an Americanist too.
2. It's a MPhil, not a DPhil. Don't concern yourself with it, just do the damn coursework.
3. Not really, so long as you complete the app, I wouldn't think it matters.
4. The UK is way more expensive than you think it is. Forget the tuition/funding, think about living expenses. Funding is always competitive in the UK, so you're going to fight for it one way or another.
