|You should consider a device made for such use like hotels or coffee shops. |
Look at Untangle first. It has a free software solution but both pay and hardware exist to protect you and your customers. There are many other products and software that are similar and do more or less.
You can't risk a customer downloading the wrong kind of stuff. You can also protect your lan with such a device.
Playing to the angels
Les Paul (1915-2009)