Motherboards generally have more then 4-6 ports on the rear. You can also just get a USB hub and run all your devices off of one port. All going through the same controller chip in most cases, so there is no performance difference.
Probably requires USB 3.0 because the keyboard itself acts as a USB hub, keyboard communications generally only require USB 2.0. Either way, the solution above will take care of it and probably be preferable to plugging all the mess into the front of the computer.