I would suggest that you build strong foundations whenever you build a PC, i.e, CPU, Motherboard and RAM. rest you can add/upgrade down the line, but if you have to upgrade CPU, motherboard or RAM later then these three things are inter-connected for not just performance but also compatibility. Graphics card, HDDs are upgradable/expandible.
I would recommend 3rd Gen Ryzen as there is a lot of performance upgrade from 2nd gen to 3rd Gen.
3600 is a sweet spot for price to performance in gaming so look into that
if you select 3600 then get a B450 motherboard as X570 boards will be expensive and overkill
3rd Gen Ryzen likes fast memory with low latency, so get 3600 Mhz RAM with lowest CAS that you can afford, e.g., 16 GB, 3600Mhz, 16-6-16-36
For boot drive get a NVMe with highest Read/Writes that you can afford, e.g., XPG SX6000 Lite 512GB