2) Aiden x Rei or Minami x Rei
Cause I like them best. I think it's because Jun x Rei & twins x Rei are more erotic by definition, so naturally I'm more curious about the other two. That and I like improbable couples - age gap, Aiden is/was married, Aiden is Rei's boss, Rei is Minami's tutor. They also seem like they would be more romantic and less sex-driven? Or maybe that's just my impression and it'll turn out the opposite.
4) I have loads. The art is awesome, but what I'm looking forward the most is the story. It's got me so excited, you can't believe. Like is the Doctor one of them or not? If yes, I suspect every single one of the characters (minor ones included). On one hand I want to know, on the other I don't want spoilers! The wait is killing me enough as it is.