What’s the easiest way for a motivated amateur to get that set up?
There really isn’t an easy way. You’d have to run the Windows VM within Linux then assign the PCI device (your GPU) to the VM. Look up gpu passthrough if you really want to dive into it. I find it much easier to just throw a second drive in the machine for a Windows install and dual boot. If you want to dual boot with Windows, make sure Linux is installed first and on a different physical drive, unless you want to be sad later, and by sad I mean learn how to unfuck your Linux install after Windows overwrites the bootloader due to some random update.