Would the (ASRock Rack C3558D4I-4L Mini ITX Server Motherboard 4 core SOC) work for a pfsense Firewall Appliance build?
Almost any x86 system can be used for PFSense. Normally Intel NICs are recommended, this one uses the Marvell 88E1543. The NetGate SG-3100 uses Marvell NICs though so I suspect it will work well. A quick google search shows that there were issues with MTU greater than 4078 in 2014, but they look to have been resolved.
Awesome, and thank you for your quick response.