Well, what are you going to be streaming?
----Casual----
If you are streaming something like making cookies, or i've seen people streaming themselves drawing for example, you can get away with 4GB of RAM and a few different apps for viewer counts music, whatever. But note Windows 10 can chew right threw 4GB fairly easy so with 4Gb keep the browser tabs down to a minimum, 720p 30fps should be very doable if all you are doing is using your webcam and talking. The CPU isn't as important, but its still has to be able to handle rendering, you can get away with a old i3 if you are going this route.
----Gaming----
Now gaming well, I like to say 16Gb will pretty much allow you to stream even the most demanding game, thats if the CPU can...