Hey there, I'm currently running FSO with all the graphic stuff except SMAA turned on on a 2GB GTX 770, 1920x1080 and I can also say that the performance isn't bad at all. 60FPS most of the time, with the really huge battles (I mean The Aftermath Reboot level huge) requiring me to turn shadows off.
As for the CPU, any FSO mod should be able to run just fine on any modern CPU that isn't some super low energy mobile part. For reference, I'm using a mildly overclocked (@3,4GHz vs stock 3,0GHz) Core 2 Quad Q9650 and I don't really see any big bottlenecks with this part - I'd say that it lets me run my GPU at over 80% usage on average. Not only the cheapest Ryzen on the market (Ryzen 3 1200) blows my CPU out of the water, but actually even the Athlon 200GE outperforms it, so technically any modern CPU will be doing just fine.
If you are tailoring your PC build expecially to accomodate Freespace, remember that FSO utilizes only a single core (with a slight amount of help from a second one), so you can aim for a low core count part with high clocks. But at some point the GPU will be more important so you can save up some money on this one.
As for the RAM, anything starting from 8GB will be absolutely fine to run heavy FSO mods with multiple background programs. I'd say you can even manage with 4GB but that's crazy levels of cheaping out
For reference: GTX 770 vs 1660Ti
and Q9650 vs R3 1200