With that many wireless devices, using 2-3 access points might be advisable. Get some old routers, turn off DHCP and give them IP's like 192.168.1.2, 192.168.1.3 and so on (if your main router is ...
Even if it works well, most experts recommend replacing your Wi-Fi router every five years. Instead of trying to convince someone to take a five-year-old router off your hands, you can turn it into an ...