You already have a huge amount of advice from the community, I'd be pretty much repeating them.
But I do have 1 useful tool for you; if you're actually going to get down to getting the PC parts, check out this site: https://pcpartpicker.com/
It helps to put things together (virtually) and finds the best prices for the parts. There are also some community built systems that you may like.
One piece of advice that I have that others have not mentioned is: Don't knock off AMD CPUs. The Ryzen line up is really good, especially for streamers, but more important is AMD's commitment to using the AM4 platform. If you get an AMD system (motherboard/CPU) now, when the Ryzen refresh is release, you can still use the same motherboard. With Intel, due to software-based blocked from Intel, if you get a Sky Lake/Kaby Lake system, you cannot upgrade to Coffee Lake, you will need a new motherboard. It's most likely going to be the same with Coffee Lake to Cannon Lake (the next generation of Intel's 'i' series