I would be temped to go for the 9 3900x - it’s got more physical cores (12) virtually 24 threads.
One think to check is your motherboard is not going to bottleneck your cpu or gpu. Get the best you can afford - if you can get newer chipsets that support PCIe 4.0 and DDR4 - AMD tend to rely on fast memory to reduce latency.
Kontakt wise ideally you want fast storage - if you can stretch to it SSDs or maybe hybrid drives it will help or a fast traditional HD. Get plenty of memory as well.
A multithreaded cpu will really be good good for plugins that are cpu hungry like synths and reverbs and it’ll mean you can run more tracks.
I helped a friend build a pc recently for 3d graphics and the ryzen are definitely more bang for buck than intel at the moment. Do your research and get components that work well together ( for example some motherboards will only support upto certain clock speeds for memory etc). Are you thinking of over clocking - if you do make sure you have a good power supply and cooling.
Getting a better cpu build components will future proof you to some degree as well.