Hi Laura,
bridge@HWC is the mode were the wireless traffic from the WLAN Guest is transported from the AP within the managment tunnel (CAPWAP) to the HWC (HiPath Wireless Controller - an old term) and then is bridged to a VLAN on the ESA port.
I don't use the VNS wizard as it includes only limited features (to make it easier) so I'd create every building block (=topology, roles, WLAN service, VNS) separate without the wizard.
Interface IP - the IP of the VLAN/WLAN interface of the controller - as it's bridged the wLAN with the wirless clients and the VLAN on the controller ESA port are in the same subnet
VLAN ID - the VLAN ID which is used on the ESA port = the wireless traffic is forwarded to this VLAN on the esa interface.
I'll post a example for a guest portal later on.
BTW, you should upgrade the controller to get the Extreme logo