Safest way imho. Set tasks in report mode, restart them. Verify after 15/30 minutes if the MSMQ and storagequeue is empty. A5 can contain items. If empty, set backup mode on indexes and stores. when backup is set, stop ev services, backup SQL databases. Verify backup is correct and usable. start upgrade. If upgrade is ok, create new backup, then clear backupmode, verify all is well, then clear reportmode on tasks. If upgrade fails, restore databases, re-install EV 10.0.3, start services etc, verify 10.0.3 is ok. call support.
Backup is key!