4.4 is out of support and does not get updates anymore, i would recommend upgrading or at least use 5.x for your second node
adding them both to the same domain
what exactly do you mean by this?
then connecting it to the NAS to restore if needed?
having 2 clusters (or single machines) connected to the same storage is always dangerous, as we assume that all pve related things (like backups, vm images, etc) belong to only
that cluster/machine. e.g. if you have a node A with a vm 100 on nfs, creating a vm 100 on node B (with the same storage) works, but if you delete the vm on either node, all vm disks for a vm '100' are deleted
also there is no locking mechanism across hosts/clusters so you could come into a situation where both nodes try to access the same vm image at the same time