What should I upgrade first?

[Highfashion]

My current build is:
CPU: amd phenom II x4 955 black edition
Gpu: xfx Radeon 6870
Psu: corsair gs800
Ram: 8gb of hyperx fury ram 1600mhz
Motherboard: Msi 870A-g54
Case: nzxt phantom black full tower

I am having trouble figuring out which to upgrade first.
If I get a new CPU I would have to replace my motherboard as well.
I was considering getting the ryzen 7 1700 and the msi b350 motherboard.
On the graphic card side, I was considering getting a rx 580 or gtx 1070. Should I replace my CPU and motherboard now or replace them later and get a better gpu.

Note: I play on 1080p and on my computer, I video edit, do Moderate gaming, and program.
In the future, I also plan on using unreal engine 4.

 

[Lutfij]

If you get the new RyZen platform you're also going to need new ram, i.e DDR4. Your current ram isn't compatible. If you're talking about a 1080p monitor and games, you'd be better off buying a GTX1060 6GB version or a little lower to GTX1050Ti. If looking at AMD's camp, you're going to be fine with the RX570/580.

I'd suggest getting the CPU, motherboard and ram and then buy the GPU later. By that time you're probably going to see a better candidate for the GPU.