provided there's enough "oomph" in your NAS box or microserver running a couple or even a few more VM's on these can be a great idea - especially if you only need to access files, do backups and run a few apps like OFFICE and some possibly corporate apps.
To access a Windows VM run this way you don't actually need to have an account on the HOST - in fact nobody need be logged on at all.
You will need a user account on the VM of course - and it can easily be accessed by RDP from another machine / tablet / phone.
I'm not sure if a dedicated QNAP server can install a VM but if you set up your NAS server using any reasonable Linux distro then by installing VBOX / VMWARE or even KVM/XEN (nearest hypervisor equivalent to HYPER-V in Windows) then you can run your VM's easily enough.
In some ways file sharing is easier since you are already logged on to the remote VM so other than screen stuff you don't need to sling across data from the remote files to your local machine (unless you want to of course).
Note though if you want to access these VM's from OUTSIDE your network you'll have to enable port forwarding to each individual machine. It's done easily enough - since on most routers you can enable DHCP for general logons (wifi smart phone / TV's etc connections) and assign a few FIXED loacal IP addresses for the VM's.
I've found my HP microserver which I'm using as a NAS box runs 3 VM's without any prob whatsoever -- one XP, one W7 and one W10.
There's a nvidia card in it so I do have sound and decent graphics too and the RAID makes the I/O nice and quick. Am going to upgrade the SSD I've got in there where my OS runs (Centos 7) but going to swap that for a 1TB SSD to store the VM's on too.
Things like PLEX / SQUEEZEBOXSERVER etc work just fine too even when the VM's are active.
You'll need decent wifi connection for the RDP - but even if your OUTSIDE internet is not the best your INTERNAL wifi should be fast enough - check what you can do on your router.