1: Before.
2: Disk2VHD works but needs to be tested beforehand. Image software by Acronis or StorageCraft would work too.
3: H-V Server 2K8 R2 has USB pass through abilities so you can attach it directly to the SBS VM using a SCSI adapter. Gives you hot swap.
4: In our experience, the built-in SBS 2008 backup is excellent.
5: NIC 1 = Management, NIC 2-4 = VMs. Bind in Hyper-V and remove host access to NICs.
6: Yes. Gives you portability.
7: H-V should be a member of the domain, but that makes things tricky if a full power down occurs. We put in anything from an Atom based box and up depending on needed roles with DC or RODC to provide authentication for the H-V host.
Philip