Users only need a connection to the internet.
I was originally wanting to split this SSID up into smaller broadcast domains as it is currently one large broadcast domain. This may not be needed now with Layer 2 Isolation enabled on the SSID. (This was not enabled before on the current Guest Wifi SSID.) So, now I'm rethinking the approach. I may leave the Guest Wifi as a large broadcast domain.
From the logs that I've been able to review, we have had as many as 1000 concurrent devices on this SSID across all our library branches (there could potentially be more at certain times of the year), so I'm not sure how many simultaneous users the Meraki DHCP server can handle. Being it is a /8 network, I would assume way more than I need to worry about.
However, I did read in the documentation that roaming between APs could be an issue with TCP-utilized services as the public IP address uses the IP address of the AP the device is connected to, and connections will need to be re-established if the device roams to a different AP. I could see this being a problem with streaming protocols like RTMP. The likelihood of it happening is probably low, but it's still something I'd like to avoid, if possible.