Check out raspiblitz' backup scripts. It has a few good methods for doing backups. USB is the most common, but I personally really like the nextcloud backup.
Discussion
Will do. I really just need a list of files to backup and restore. Then I can add them to my ansible variables and roll out the borgmatic config.
It's the testing that will make me a little nervous, mostly just because I don't 100% understand how all this works yet.