Windows guests also run fine on KVM, use the Virtio drivers from Fedora project.

There are several solutions but will be above the budget. Best solution is the Argon Eon case for the RPi 4. I’m waiting for a version for the RPi 5.

Can house the Pi and either 4x 2.5" drives or 2x 2.5" and 2x 3.5" drives, all SATA.

Have a look at NewPipe app, might be of interest.