Nowadays is easy to find a board with more than two ports. For a box with 4 gigabit ports, one used as WAN, others act as as LAN as if they are all part of a switch. Bridging is a good way to go.
A bridged interface is one that can filter traffic without pfSense being involved in the IP layer of the connection. This is commonly referred to as a "transparent firewall".
pfSense box with multiple NICS; 1 for Wan, others for Lans (two or more).
What we will get:
i port as 1 WAN, Others as LAN.
Step 1: Assign an individual IP for all NICs by going to 'Interfaces → Assign'. Important!
Note: Only set up a IPv4 address for each NIC.
Step 2: Set up DHCP on NIC1 by going 'Services → DHCP server'
Step 3: Bridge other NICs by going to 'Interfaces → Assign → Bridges' and set up an IP for the interface.
Note: Do not include WAN and NIC1.
Step 4: Create a interface groups by going to 'Interfaces → Assign → Interface Groups'.
Note: Include all NICs and Bridge interface in "Member (s)", do not include WAN.
Step 5: Change the default firewall rule under NIC1 to all NICs interfaces to avoid being locked out by going to 'Firewall → Rules'
Note: Change the Interface from NIC1 to the Interface groups which is created in Step 4.
Step 6: Enable DHCP on the bridge interface by going to 'Services → DHCP server'.
Step 7: Disable DHCP on NIC1 by going to 'Services → DHCP server' and include NIC1 into the bridge which is set up in Step 3 by going to 'Interfaces → Assign → Bridges'.
Step 8: reboot and test.