Generally speaking, the hardware allows for a high number of simultaneously enabled SSIDs.
Because each activated SSID (even when idle) has a negative impact on performance of all SSIDs, the maximum number of SSIDs any device will simultaneously broadcast is limited to 4.
To strike the balance between performance and advanced SSID features, the Plasma Cloud Console allows to create an unlimited amount of SSIDs which can then be assigned to individual devices in the same network. Thereby allowing some devices to broadcast SSIDs different from other devices to accommodate setups in which this proves helpful.
Multi-SSID Performance Impact
With each enabled SSID, the Access Point needs to send additional beacon broadcast frames and respond to probe requests. These frames are part of the WiFi network discovery process, thus are required before any WiFi connection can be established. Consequently, each additional SSID causes more management & discovery frames to be in the air and leaving less time to transmit actual data. The team at WiFi revolution has published an excellent SSID overhead calculator visualizing the performance impact of multi-SSID deployments.