Most sub 100 cases have only 2 front USB 3.0
As for how do you connect them? the front panel has an internal cable that you plug in the USB 3.0 header of the motherboard, that is all it takes.
USB 3.0 only makes a difference in data transfer with devices that are rated to work at that speed as well, most of them only external storage drives. For USB 2.0 devices, 3.0 makes no difference.