For a while I used a post-backup script that copied the job Database to an alternate location, but I stopped doing it when improvements were made and bugs fixed in the database recreation process. You can test the recreate process yourself to see how quickly the database is rebuilt. You may find that doing separate backups of it is unnecessary. If you DO decide you want to back up the database, it’s important to do it after every backup job.
Keeping exports of the job configurations is very helpful. I would resave the export any time you reconfigure the backup job. You can also consider backing up Duplicati-server.sqlite. It contains all job definitions and global settings. (Global settings are not saved when you export a job config.)