as for pcie slots, It depends on how many ports you want to have. The more ports you want the more pcie lanes you'll need. to expect a pcie slot to support the full bandwidth of usb3 you would need 10 lanes per port. 1 pcie v2 lane is 500mb/s and usb3 is 5000mb/s you see. A good coomprimise is a pcie x4 lane card with dual controllers for 4 ports. or a 2 port single lane card with 1 controller.
If you're not planning much really high speed stuff like usb ssd's then a 4 port x1 card might do for you, for slower things like printers, modems, mice, keybds...