Yes, you can install Windows 8.1 on a USB 3.0 drive.
Yes, you can install Windows 8.1 on a USB 3.0 drive.
It seems Windows 7 doesn’t support USB 3.0 at all. You can only use USB 2.0 ports with it.
I believe Windows 7 isn't capable of handling 3.0 drives, though I'm not entirely certain.