So, basically you are trying to setup a plain vanilla pfSense and additionally you want a wifi access point in bridge mode with your LAN subnet.
Start by setting up pfSense and make it work. If your hardware is right, your install is right you should have it up and running in no time.
At that point you should have nothing but a WAN cable from your pfSense box to your Internet Modem, and a LAN cable to the network switch box. (and a computer connected to the network switch with an ethernet cable - NO WIFI YET, that you would also use to run the WebConfig on pfSense)
You may want to check that pfSense's console shows your public IP on the WAN side and your LAN private subnet address. You should be able to ping any public server out there assuming that they are willing to respond. Try to ping www.grc.com, it should resolve to a public IP address and give you ping feedback. The same way, you should be able to ping any computer on your LAN by IP address.
If any of these is not working your pfSense is not properly set. Go back and check your dynamic ip settings on the WAN, the static IP setting on the LAN, the DNS server addresses, your DHCP server settings on the LAN side (if you're using DHCP for your LAN side computers/devices)
Again, until everything said above is working flawlessly do not even touch to wifi, access point, etc. You are in the wired ethernet world right now.
Once you're done with the above, it's time to leave pfSense alone!
Now, setup your wifi access point whatever that is. Linksys with dd-wrt in bridge mode I understand.
So, you should have only one single wire connecting your wifi A/P to the network switch box. It might go to the WAN side or to the LAN side of your wifi box (Linksys) depending how the bridge is built with dd-wrt.
Work on it until it is fully functional, meaning that with a wifi connected computer you should be able to ping, and access any computer on your local network.
If you're not there yet your problem is isolated to dd-wrt and Linkysy wifi box. Just focus on it, do not change anything with your pfSense config. Do not waste your time trying to access public servers on the internet, etc. You should be able to see your own LAN first before you get any internet traffic.
When this much works, you should also be able to ping the LAN side of your pfSense router.
So try to ping your static LAN IP address on pfSense. If everything is done, next try to ping some outside, public servers like www.grc.com (from your wifi connected computer/laptop).
Well, you should be done by now.
Edit / Addition:
If you get to make everything work and after a while you notice that you can no longer access the internet via your WAN, check pfSense's console for dynamic IP loss with your internet provider. If that's the case try to reboot and try to figure out if it is going to loose its IP again and how much time after reboot. Repeat your test a few times until you have a firm idea that this is happening over and over and within a certain time-frame. Meanwhile do not change any other parameters/components in your overall system. If you consistently loose your IP, it's likely that you have a NIC problem (hardware or device driver -wise). Install a new, maybe different type of net interface, reconfig pfSense's interfaces and start testing again.
The WAN dynamic IP loss scenario is what I experienced repeatedly when I was trying to use a USB/Ethernet adapter.
Hope this helps.
Halea