In terms of RAM, you will need 8GB however you will be needing a strong CPU since all encoding is done with the CPU. however, you would only need an iGPU or basic GPU since you will not use that hardware to capture any feed from your gaming rig. you can use 1 screen but this would mean you will have to change feeds what is suboptimal and you would have to set everything up before starting a stream and or recording. You can start out with a very cheap 2nd hand pc with cheap mice and keyboard as well as a screen. You will need a 2nd PC, this can be any PC or laptop the better, of course, will result in better footage as well as being able to stream and record at the same time if you are a content creator as well.
OBS and NDI streaming and recording tutorial.