so can i do a rig with an AMD cpu and a nvidia graphic card? any downside with that combination?
That would be pretty much the best combination really in terms of bang for your buck imo, I have 2 different systems which use Ryzen Cpu's and Nvidia Gpus and they're both great little machines. Ryzen1700 with a 980ti and a Ryzen2600 with a older 780ti both machines very capable at 1080p gaming which is all my monitors and projectors use.
Fancy hearing me on an amateur podcast with friends gushing over one of my favourite games? https://youtu.be/1I7JfMMxhf8