Is it your wifi strength at fault or your bandwidth? For instance if all devices connect OK, and don't disconnect then it is probably more to dowith the fact that you dont have enough juice to supply all your users. The only way to improve that is to upgrade your subscription to fast package 10 mbps or faster, or put in a second broadband line. Of course you could limit who uses the broadband and when.
Yes well forgive me but most people don't know there arse from their elbow when it comes to WiFi, and from your description I would say that fits the bill. Your standard router can handle 255 devices on one router no problem, as long as they are all in range. Good luck.