Using a L3 Switch to expand a pfSense device

I’ve been experimenting with pfSense on an old, power-hungry computer and would now like to install the software on something more practical.

I'd like to connect three separate LANs to the pfSense, and so as a minimum it would be good to have at least 4 RJ45 ports (1 port for WAN) . Unfortunately, the official pfSense boxes are quite expensive here in Europe when you add tax and delivery to get the final price.

As a half-price alternative, I was considering a mini-PC with 2 Intel RJ45 ports. Could I plug a small Layer-3 Switch into the second port and still be able to keep the three LAN networks separate? Although the LANs should remain separate, two of the LANs would need to be able to talk to each other. What level of complexity would this switch add to the pfSense setup? Is this a feasible task for a beginner?