There are no upper limits on this type of device other than what you impose yourself. I'm assuming that you mean the number of available WiFi Connections that you can run.
But in theory you could have 2,000 or more WiFi Connections and other than being [b]Painfully Slow[/b] to download anything off the Internet it would work.
If you are asking how many direct wired connections you can have that is simple 4 as that is how many Ethernet Ports that there are on the device. That of course doesn't mean that you couldn't Daisy Chain those 4 Ethernet Ports to Hubs/Switches and continue out to however many you actually need though. ;)
Col