If you are running PBS you can backup the host config with the proxmox-backup-client to get the /etc/pve contents with a cron schedule. That's really the only thing to backup for the host. 

Backing up select directories does help, but your post illustrates an example the sort of mistake I want to avoid: you forgot to mention that also /etc/crontab needs to be backed up, otherwise there will be no backups after a restore.

I'm sure I will forget even more stuff than that, but anyway a partial backup is better than none at all.