You should be fine in doing in place upgrade. I take it you tested all the add on products and dbs on the new version?
Naturally I would back up everything.
Make sure Notes service (s) are disabled and reboot server before upgrade. This prevents a file / process in use that can prevent a successful upgrade.
After applying 9.01 start and stop server before apply fix packs hot fixes.
Upgrade the ods to latest version.