I'm dead tired, so I'll give you some of the skinny in list form:
1. No, it's not import friendly. They tease you with a little bit of English on the menus as they scroll down, but before you can make it out it's faded into kana. If you're not familiar with kana at all I'd steer clear for another few months until it comes here.
2. Yes you can make your own music, and yes you can hum, whistle, or sing into the mic and the software will recogize and record the note.
3. Yes it comes with headphones but they're awful. I wanted them out of my ears as soon as I'd put them in.
4. The mixer CD is used to scroll quickly through the songs you're tracking (think ipod). I haven't come across it doing anything like scratching.
5. Yes, it's coming to the US.
6. Yes, all of the anime theme songs will probably be axed.