Do you want to limit the number of clients connecting to the SSID or AP?
The option is available on the Access Points >> Click on WLAN Group >> Model Specific >> Max clients allowed.
For the SSID Wireless LANs >> Advanced Option >> Max Clients. This is Max clients per AP radio to associate with the SSID.
Check out the below link for your reference.https://support.ruckuswireless.com/articles/000001980
Let me know if the requirement is something else.