Comcast router and modem
How should I configure pfsense if it's running behind a comcast router and modem should I turn off Dhcp on my wireless router?
See if you can enable 'Bridge Mode'. Please note doing so, will disable the wireless access point that is built in the router/modem combo. You will also lose access to the configuration page within the modem. By putting it in bridge modem, your public WAN IP will be provided directly to the pfSense WAN interface and you wont have to deal with double NAT issue.
I have a TWC modem/wireless router setup myself. I wasn't able to put it into bridge mode since the admin configuration page was locked out to the customer. Tier 3 support was able to put my modem into bridge mode remotely. In their billing system, they removed the wireless option, which automatically puts the modem/router into bridge mode.
If you need to take it out o bridge mode, either a call to customer support or do a factory reset to the modem should bring it out if you didn't have them remove the wireless option in the billing system.
If you want to still use their wireless function in the router, then disable DHCP, look for a DMZ setting and enter to the IP address that is your pfsense router… But be prepare to have issues with NAT. Game consoles come to mind, uPnP wont work correctly either..
I'm running pfense on a old laptop. Should I get a usb wireless card for it and run it bridged? Or can I get a usb to ethernet adapter and use my Linksys ddwrt router into pfsense and get wireless? If not what kind of wireless card should I get? All While still running behind comcast bridged
I would go with the ethernet adapter route… Hopefully your laptop has a built in ethernet port since you'll you need 2. Connect one to your cable modem and the other to your ddwrt router(make sure its setup as a wireless AP only, no dhcp). The ddwrt router with act like a Wireless AP and a network switch. The only issue I can see with this setup, could be network throughout but I haven't used a usb ethernet adapter in very long time (8+ years).