I haven't had to "consider" too much in the E2K3 to E2K7 / E2K10 migrations I've done, personally. I've basically just left things as-is and moved the mailboxes.
If you're moving a ton of data I suppose you might enable circular logging on the destination server-- gauge your free disk space and decide if that's something you need to do. I've found that my E2K10 servers are typically so much more I/O efficient than the E2K3 servers I'm migrating from that leaving antivirus enabled on the destination server makes no difference. On the source server you might see a speed improvement, but I have no specific metrics to report.
None of my Customers have had problems with resource accounts after migrations so I haven't done anything special (both in E2K3 to E2K3 migrations nad E2K3 to E2K7 / E2K10 migrations). All mailbox access is supposed to dereference the mailbox store through the
homeMDB property of the Active Directory object so the physical storage location of the mailbox should be irrelevant (and it has been in my experience).