Dear Sir
1) Yes, or a main-board with two Ethernet port, three to keep internet on your box.
2) Correct
3) We have been using FMC104s to test FMC204s but not completely sure about the details, once again this interface is not suited for anything else than offloading snapshots.
4) I remember that, this was about having a different Mac address.
5) It is impossible to tell, we have not carried this modifications ourselves.
6) This is possible, delivered "AS-IS", without source code level support.
I think it would be wise to decide if Ethernet is really suitable for you, what kind of reliability do you expect. Talking to one of our sales engineer will provide you with some engineering feedback.
Best Regards,
Arnaud