The answer is that it depends. Things that influence a roon core are;
Library size (local + any streaming tracks)
Type of DSP (upsampling PCM is a lot less demanding than DSD, for example)
Amount of DSP (upsampling to DSD, applying convolution, applying EQ, etc.)
Number of simultaneous endpoints playing
And, they influence both CPU and RAM requirements. Most users, I imagine, would be fine with an i5 and 8 GB of RAM. But, if you can give more insight into points 1 - 4 above then maybe a more focused response to your initial question.
It is more than capable of running Roon. It is actually comparable in performance to a first generation Nucleus + although the single core performance of the Ryzen is a little slower. It is a pretty good pick and should work well as a server.
Anytime you add a track to your library, it adds to the database load. Does not matter if the track is local or streaming. So, when factoring what cpu you might need, the total of local AND streaming tracks in the library need to be taken into account. And don’t forget to plan for growth.