would be a good idea to test the backups on 7, and double check the release notes, they hold just about every caveats. The 7to8 upgrade was not horrible, if you have backups, you could always attempt the upgrade after taking backups, then if successful take new backups, test, then install new drives and restore. depends on how paranoid you feel.

If this was a production system, that is probably the change plan i would follow, but in production I would also be able to migrate VMs. I am not nearly as careful in the home environment.