But with i5 7600k and gtx 1070 you will probbly run the game with low AA means fxaa. And its fine as 60 fps stable????
I don't think COH2 does FXAA, just MSAA. I could be wrong, but you can definitely disable it in-game and force FXAA through the Nvidia Control Panel.
A GTX1070 will be very underutilised as the game goes on. The game engine is just very poor at using CPUs properly (similar to PUBG), which means the GPU doesn't get enough instructions to keep it running at full capacity. You'll notice very little difference between the two CPUs you've mentioned. I'd go for the 6-core just for the advantages that those extra cores will provide in other applications and games.
As others have mentioned, the larger the map and the longer the match runs for, the more your CPU and FPS will choke. That hardware should keep 1v1 matches reasonably above 60fps for most, if not all, of the game though.
No need to upgrade your CPU. COH2 is more GPU heavy anyways. Your CPU wont limit your FPS
Uh, no. The exact opposite. The only time any modern GPU is likely to struggle in this game is smoke and fire particle effects are happening, which is very much another optimisation issue.