There is/was a Kodi Backup add-on in the Kodi repo. I've never used it, but it might be worth looking into. It probably backs-up only to a "local" filesystem path, so to save off-box you'll need to configure a persistent SMB mount (there are instructions in the wiki) so there's a local filesystem path under /var/media/ to the remote NAS share.
The backup function in the LE settings add-on also captures /storage/.kodi, /storage/.cache, /storage/.config to a tarball which is saved to /storage/backups. Unless you are locally storing media on the SD card which needs to be preserved those are probably the only folders which need to be backed-up. It doesn't handle movement of the file off-box though.