Why would you change the GPU? The RX 570 comes with ShadowPlay which is great for recording and streaming. It is also a great 1080p gaming card. If you were wanting to change it, there is nothing in that price range that can even touch it, so you'd be paying a lot more for a meaningful upgrade.
The Ryzen 5 2600 is a good CPU, buuuuuuut the 3rd gen Ryzen products launch on the 7th, so you might want to wait. Also, 8GB isn't a lot of RAM in this day and age. We are at the point where 8GB is the minimum that should be considered.