You don’t say anything about the client machines but in general I’d very much avoid trying to reinvent the wheel especially for critical systems like backups. I

You don’t say anything about the client machines but in general I’d very much avoid trying to reinvent the wheel especially for critical systems like backups. It’s hard enough to do right so adding another layer of hacked and glued together software is not what you want. Can’t you use Carbon Copy Cloned or TimeMachine and set them to start the backup as soon as the disk is attached? Just add a calendar event to notify the user to bring the disk home from time to time.