Connecting 255 computers to a single WiFi access point, while theoretically possible, is not recommended. Performance of such a network will be very poor. Install multiple access points instead to distribute the network load. By adding more access points to the network, effectively any number of computers can be supported (though the network becomes progressively more difficult to manage).
On a home network, while dozens of computers and other devices may connect to the router, the performance of a shared Internet connection will quickly degrade as more computers access the Web simultaneously.