Intel will always offer the best FPS for the player and its close in terms of FPS for the Viewer . At ultra wide 1440p ryzen 2700x doesn't lose ground to i7/9 for non streaming gaming but with ultra wide 1080p there is a bit of a gap . From 1440p onward Ryzen closes the performance gap and more about GPU power.
New RTX cards allow for better encoding so that is another route - specially picking up ryzen 2600X or i7 9700k to keep down the costs ! Turing cores have advantage over Pascal with H265 encoding .
all depends on your budget , would deff push Gigabyte z390 board at £120- is entry board but its a lot better then most z370/390 boards like Asus 370-A.
Noticed you've gone for corsair parts. Their rep started to lark more on here and has confirmed their RMA policy is to replace units with Brand New rather then attempt to repair it ! RMA team is also UK based (woking if i can recall visiting samsung and seeing corsair office)
would personally pick ryzen 2700/9700 and sink extra cash into GPU