Assuming I go down the 2 bay, raid 1 route would I be able to hot swap the mirrored disk once a week as a backup strategy?
I'll try to be brief but if not ...
Technically you could but you wont want to do this because:
1) Most 2 bay NAS require trays for drives meaning you need extra trays or unscrew the drive from on of the trays etc.
2) You would have to each time reconstitute a mirror (takes time depending on amount of data and drive)
3) Most of the two bay NAS units are not intended for "rotation" though they can technically do it)
4) While some might say different, greatest potential for errors is in (re-)constituting a drive as is physical drive issues.
If you continue the NAS route, consider an external drive (not unlike what you are doing now) and back up the NAS to that drive that will be used for off-site rotation. While I use/have NAS storage, for off site, I would never consider removing a drive from a NAS but as stated, back up the NAS. I consider the NAS both storage and local backup of computers only. If my computer drive fails, I use the NAS to reconstitute the data after the computer drive is fixed/replaced.
Last - years ago, I worked for a company that had tape rotation. They put the tape drive in the server dedicated to storage server. When anything went wrong with the tape or tape device, they had to shut down the storage server (take it off line) and then get the tape backup unit working. I opted to take the tape device out of the storage server as a stand alone device that was connected to the storage server. This allowed the storage to continually back up the multiple desktops without issue and kept all "shares" active. When the tape drive failed, I could disconnect it and fix it and bring it back up on line without any issues. Ultimately, every company branch did the same thing by extricating the tape drive (used for off site storage) from the storage server. Hopefully, the analogy is clear here.