It’s absolutely possible. My recomendations: Do not boot an OS from a USB stick, USB sticks are made with recycled donkeycum and will quickly fail when reading/writing as much as an OS neeeds to. I’m sure there is a boot loader that can help you choose wether to boot into windows or your NAS OS everytime you reboot.

It’s not frowned upon, it’s just not made for it. It’s made for desktop use. It’s also more unreliable/unstable, just ran into some problems yesterday after updates. You DO NOT have to pay for a license however. The only features of windows you lack (afaik) on an unlicensed install is desktop customization and some kind of remote access that I have never used myself. Docker and VMs will work equally well on windows.

Don’t be discouraged from using a dedicated NAS operating system though, there are a lot of videotutorials and documentation. Worst case scenario you wipe it and start over with windows.