I figure the most bang for my buck right now is to set up off-site backups to a cloud provider.

If you don’t have the budget for on-premises backup, you almost certainly can’t afford to restore the cloud backup if anything goes wrong.

Then I started reading about backing up databases

Go read the instructions for your database in particular. They are completely different from each other. Ignore generic instructions.

now I’m configuring a docker-db-backup container

What is perfectly fine. But I’d first look how this interferes with the budget you talked about earlier and if it wouldn’t be better to keep things simpler and put the money on data replication.

Either way, if your budget is low, I’d focus a lot on making sure you have the data when you need to restore, and less on streamlining the restore procedure. (That seems to be the direction you are going, so yeah, I’d say it’s good.) Just make sure to test the restore procedure once in a while.

Enough to make a RAID 6. As few as possible.