I've used the webmin before, and I think it's a great product. Unfortunately, what I am trying to do is make these 4 boxes that I have consistent with each other, so that I only have to train people on one interface. Since I have 2 pfSense boxes already, this is the way for me to go. I think it's great that these boxes are this flexible.
Fortunately I don't need an elaborate DHCP server, just the basics + reservations and lease viewing.
What I did for this particular box is install pfSense onto it with 2 NICs installed. Once the install was done, I configured the LAN interface with the LAN IP, and in the WAN, I put 0.0.0.0 as the IP, and for the gateway, I put the IP of the LAN gateway. This changes the routing table so that the machine can get to the internet for NTP, etc... I'm actually kinda psyched that it works this way! The LAN interface just sits there with nothing plugged into it.