Could someone give me some parameters as to what I would need in my computer in order to have quality streams (basically minimal lag/buffering) with 2-4 windows open in OBS?

well what quality are you looking for? what are you intending to record/stream?

You havent really given us a lot of info to work with

Just to give you an idea, my streaming computer is 7 years old and streams pretty much everything wonderfully.

It has the following: i7 Intel, 6 cores 24gb of ddr3 1066 ram NVidia 760ti GPU A solid state drive over a sata connection

In 2011, it was state of the art. Bought it as a present to myself after heart surgery. Now, my work laptop beats it handily at nearly everything, including gaming.

Point is, anything with a recent i5 (or AMD equivalent), 8gbs of RAM, a halfway decent GPU, and a solid state drive is very capable for streaming. Unless you are trying to play cutting edge PC games at max settings (which for speedrunning is a terrible idea anyways), it should be fine.