From Apple's support forum,
The official Bluetooth specifications state seven is the maximum number of Bluetooth devices that can be connected at once. However, three to four devices is a practical limit, depending on the types of devices and profiles are used. Some devices require more Bluetooth data, so they are more demanding than other devices. Data-intensive devices may reduce the total number of devices that can be active at the same time. If a Bluetooth device becomes slow to connect or does not perform reliably, reduce the total number of connected devices.
So depending on how the audio is digitised, you could have a problem with more than 3 or 4, but in any case 7 looks like a maximum.
However, and this is a pretty big however, you are not looking at a bluetooth device, but a 2.4GHz Frequency Hopping Spread Spectrum device. Which is what 802.11 and WiFi are. This device doesn't specify either 802.11 or WiFi, so it may not behave as well as devices with the standard specification, but you certainly have bandwidth for many devices to connect at once.
Be aware though, that there may be manufacturer limitations that are specific to them, and you'd best check to see if it conflicts or interferes with any wifi in the building.