All discussions about the open source, FreeBSD-based firewall called OPNsense.
Depends a bit what you want to do with it. Replace your router? Just apply FW rules in your LAN? Intrusion Prevention/Detection?
Make sure the Network Interfaces are performance under BSD.
Check this if you haven't already: https://docs.opnsense.org/manual/hardware.html
Almost everything works as long as the Ethernet chipset are Intel.
For the wifi is a bit (or a lot) more complicated, you will need to research.
How many ports, ram or cores is something that depends of your use case and you didn't specify
But if you want a small guidance I used a second hand sophos machine for ebay, and without idp/ips is sitting very comfortably on my home network
Don't buy shit from AliExpress.
Everything on Amazon is from the same place, just with a markup for you local burgeosee lifestyle