Only hardware device you need is a Switch, and of course at least 5 CAT 5e/6 cables. If you have no plans at the moment to add more computers, then simply buy a 6 port switch, and connect each of the PCs with it. Connect the 6th Port with a router with DHCP enabled and connected to WAN. You'll be good to go,
Which OS will you be using for all of your cyber cafe computers? Depending on that you can set networking within the PCs in your cafe.