Personally I prefer to do the backup from Windows. The way I do backups may not be appropriate to others, but there may be some useful points in here… possibly 
Firstly don’t do any kind of instant mirroring, as if you have finger trouble, or something nasty starts zapping stuff, then the backup gets instantly zapped too.
Secondly, if you aren’t backing up the backup consider making it read-only from normal Windows accounts and only writable from a separate login you only have in the backup profile.
My personal technique, using a SSD to boot and Rotating Rust for most data, is:
Image the boot drive from time-to-time, in case it gets zapped. Much easier than a re-install and finding all those licences… I use Image for Windows but it’s quite techy and there are simpler tools.
I use Syncback to backup data (including some frequently changing stuff from the Boot drive). There is a free version, the paid SE version is all anyone is likely to need, although I have the Pro version for other reasons. I don’t mind paying modest amounts for something that is so important to me. Also they have added a couple of things I asked for (maybe others asked too, but I had to push somewhat), like queuing profiles to run sequentially and controlling what happens to new files/directories that appear (back them up, ignore them, etc.).
Think about how often to back-up, as anything you’ve (or something nasty) made a bad change to will not be reversible. I have backups of the backup, which get updated not too often, so I can update the backup quite frequently and not lose stuff.
P.S. If you don’t want to get another NAS to backup the NAS’s backup then a TR-002 works well (if the NAS has a fast USB port). I just stripe the disks for maximum space and performance as disk failures are rare and you get twice the capacity, plus the NAS has redundancy. Just go put it somewhere else afterwards.