Hmm, you're pretty much into territory I've not been in, as I've not dealt with wifi on pfsense. At work we have the following setup:
ISP<--->ADSL modem<--->pfSense<--->Switch<--->Workstations
ADSL modem is configured in bridged mode so it only passes traffic through, and is connected to the pfsense box on the WAN assigned NIC. WAN interface in pfsense is configured as a PPPoE connection. The LAN NIC on the pfsense box is connected to the switch box, which all the workstations are hooked up to. The LAN interface in pfsense is configured with the ip address of 10.1.1.1/24. Then the DHCP server in pfsense is configured with the subnet of 10.1.1.0, and a specified range which the workstations will be assigned addresses from.
Remember, the LAN interface is everything behind the firewall, i.e all the clients that's gonna connect to the internet. The WAN interface is everything before the firewall. WAN stands for 'Wide Area Network', and LAN for 'Local Area Network'. So the WAN interface should be connected directly to your ADSL modem if you have. If you only have wifi access to your ISP, you should be able to configure pfsense with the wifi card you have to connect to the ISP, and not go through a second computer for it. But as I said, I've not dealt with that scenario myself, so I'm not sure.