In another discussion I wrote about connecting a router to the MoodleBox. https://discuss.moodlebox.net/d/60-connect-an-access-point-to-the-moodlebox
I can't say the maximum number of clients, but with a powerful OpenWRT router you get WiFi for many clients. The router is connected via ethernet and the router generates the wifi connections and the ip addresses. The MoodleBox wifi can still be uses for smaller groups or as a fallback connection. You also can hide the MoodleBox wifi.
Yes, I know ... with the external router hardware, the MoodleBox project is not mobile, is not independent of a power supply and is also no longer so easy to transport.