I'm experimenting with a guest network, but on adding a new ssid to the 2.4ghz network, it remains disabled, I can only get it to turn on if I disable the other ssid first, the router on stock software does support guest networks so I'm not sure what I'm doing wrong?
Also, it depends on how you want to configure them. SSIDs can be attached to whatever network you setup, even multiple SSIDs to the same network...to WAN and to LAN...to a new guest_net, to add another SSID/passphrase on same LAN for temporary users, etc...
There is no single multi-SSID config, perhaps you should create a thread describing your use case