For the benefit of other people, and since I purchased the expander already, I would like to reply to my own questions.
1) NO! The only thing they come with is a switch to switch it between -10db and +4db. But that is it. Preamp is really needed.
2) at least the 6 ins of the expander do. I do not know about the original two inputs.
3) any powered mixer. It is good value for the money.
4) For the money? there are almost none!