First off, I think it’s wise in a NAS configuration — because it invites the capability — to use some form of RAID with two drives of redundancy to at least significantly reduce the chances that a single disk error (the most damaging sort of exigency) will cause interruptions or even more major issues.
But of course RAID is not a backup defense at all when it comes to user errors!
In my configuration, I have nightly backups sent to an attached USB 3 drive. So the worst thing that happens is that, during a day’s worth of music curation work, if I do something wrong, I lose that one day’s worth of work (which usually is recoverable without a heart attack!).
I then also have a second monthly backup task using another drive that I then keep offsite (or in a fireproof safe if I can’t get it offsite right away).
As I have mentioned elsewhere, I don’t have cloud backup options available in a practical sense because of my upstream internet connection. This all works quite well for me, at least. One thing I didn’t mention in that post is that I also have a third offsite backup in a different location that I update less frequently, but it gives me a sense if option 1 and 2 fail, I don’t have to have a major heart attack.