Lol... Yeah, the new User & Device form sucks, especially on larger systems.
Actually you should be good, we have done several from 5&6 to 7 with no I'll effects. Just double check the release notes.
One thing I've found, If you have any CXi controllers they take what seems like FOREVER to come online after the final reboot of the upgrade process, some over 10 minutes to initialize the embedded PoE switch after everything else is up and working. No indication anything is happening in the maintenance terminal either, it just suddenly happens to start working... It might go faster if you call tech support and get through right away, the first time it happened the switch came up just as the Mitel tech answered the phone.