Going back through your specs...bro a 4090 costs basically the same as my whole PC that's running games at 120 FPS+ on a 4k monitor with no issues.
Check out combo deals on Newegg for Mobo+RAM+CPU, or Microcenter if you have one nearby (I don't). Your biggest factor for gaming will be the GPU. You can run 60+ FPS on a 1080P monitor on 5 year old midrange GPUs. If you need 4k res, ask on PCPartPicker forums.