Unfortunately I cant answer those specific questions bout xcp-ng. Maybe someone from vates can confirm.
it wasn't to long ago nvidia prevent users from using passing though consumer cards into vms.
Different use cases: Ceph is better with more hosts (at least 6 or 7 minimum) while XOSTOR is better between 3 to 7/8.
We might have better Ceph support in the future for large clusters.