I am thinking of building a router for OPNsense. I am familiar with building computers but I am not familiar with networking. What kind of hardware would I need to hit 1, 2.5 (my most likely target), 5 or 10 gigabit speeds on my local network?

I was thinking of buying a small form factor PC and sticking an Intel I226 Network Card or something similiar in it.

So, what kind of processor would I need?