Libreelec is a great htpc, meant to give you that same “10ft computing” experience as any other media center. Its requirements for 1080p aren’t that intense, as it runs well on a raspi 4/5. They do recommend keeping the resolution set to 1080p in kodi and letting your tv upscale to 4k if youre playing 4k content, so that is a good metric to target.
You can run it as a VM, but running 3 off the same machine loses a lot of the “media center that controls one tv” utility, unless you have 3 hdmi ports on that computer that are wired to those 3 TV and can pass through 3 IR blasters or bluetooth connections for physical remotes. If you can, it should work fine.
If you are routing IR blasters, flirc has a USB blaster and a remote called the Skip that should work out. Ive used the usb blaster with kodi and it integrated seamlessly, but haven’t used the remote yet.
So you could get 3 of the remotes, 3 usb IR blastere and whether length of usb cable you need for each to connect to the host and pass those through to the VMs.