Questions about virtualization

I've got some questions about bare metal virtualization.

Thinking about GPU pass-through, could somebody please explain how USB works. Is it like VMware workstation/fusion, when clicking on a window, then the input gets directed to this window? Do the virtual machines, even run in windows or are they restricted to monitors? And another question is, if I would switch to amd, are there the same complications running virtualized - needing a custom kernel - I would guess yes? Could you describe the experience?

Thanks