I've never installed windows on one so I don't know if you'd run into any driver or other issues but I imagine you could get it to work. you wouldn't have any of buffalo's software which at the very least means the lcd screen wouldn't work and there are probably limitations with hot swapping drives etc. I believe modern windows has software raid capabilities but I don't know any details, it might be worth a try.
I know from experience a Debian install works pretty well on these devices. You can find all sorts of resources on the web to help setup raid array and services like samba etc. I'm planning to write a short guide to setting up the raid at install time but it's all pretty standard stuff. The only really custom piece I'm working on is enabling drive bays that aren't initialized at boot
All the TFTP recovery stuff you've read about is for non-intel linux-based firmware and doesn't apply to this device.
If this were a TS-QVL (the non-windows version of the device) you could install Buffalo's linux based firmware using these guides:
https://buffalonas.miraheze.org/wiki/Create_Recovery_Disk_for_Intel-based_Terastationhttps://buffalonas.miraheze.org/wiki/Enable_Debug_modeI don't know if that would work on a WS-QVL or not and do not know if buffalo would condone doing so.