Yes, I think that version of the SanDisk microSD card is A1 rated. I don't completely understand which option is the best for the OMV system disk - microSD, USB SSD, or ?
As for backups, I will continue backing up my data through other methods. If everything goes well after some months, I may add a second Rock64 NAS which will be a copy of the first NAS using Rsync. Ideally, this NAS would be off site.