Throw away the dd-wrt router completely, pfSense can handle this all alone.
How many pots does the pfSense box have?
if it has at least 2 ports, use one as WAN, and add to another one VLANs. Note that in pfSense you can add VLAN tagged traffic to a port, while you can still access that port with untagged traffic too, and firewall rules apply completely separately: the VLAN-tagged traffic is handled as it it would go through completely new virtual network cards, so you look at them as your pfSense would have physical interfaces for each VLAN, while it doesn't have, but it looks like so. This applies to firewall rules, DHCP and all the existing services in pfSense. So you take this port and plug it to your switch as a trunk interface, you'll be able to access through the switch the VLANs separately, and that's great.
if your pfSense has jut one port, you can do similar as above, just assign WAN functionality to a new separate VLAN - you'd use WAN traffic also through the switch, but separated from the rest.