Right, so it's worth mentioning that if you have a ZoneDirector, then Ruckus provides support for Guest Networking which doesn't even require a fancy firewall/gateway with VLAN support. Modern ZD firmware directly supports layer 3 isolation such that even though everyone has IP's in the same subnet, attempts to access your subnet by guests are simply dropped by the ZD.
However, without that, you've got a SonicWall, and hopefully you have managed switches with VLAN support. So basically you'll need to set up enough VLAN support such that you can create a separate VLAN for guest on the SonicWall, and then assign that VLAN ID to the wlan that you're choosing.
Almost all of these instructions pertain to your SonicWall, with only the assignment of the VLAN ID a function of the ZF7782.