No, there is not a no-bay NAS, although there is s diskless NAS that one installs their own disks in ,or say a 4-bay NAS populated with two disks now, and the other two for a later time to expand the NAS capacity.
I would suggest buying a NAS that is not diskless; costs are similar and WD puts the correct disks in it.
To explore your options, go to wdc.com and look at the My Cloud product section for the more basic NASs and Network Attached Storage (aka NAS) section for the more advanced ones. Have fun.
Since you have all your data already on separate disks, you would not need to backup your NAS; you already have a backup after you copy all your individual files to a NAS, The task then is to keep the individual drives and NAS up to date as you move forward.
