If you've got an AM4 mounting kit for the 212 EVO, you'll be able to re-use it. It's unlikely you got one with the cooler so you'd have to contact AMD for the AM4 mounting kit, or buy it separately somewhere. The Dark Rock 4 is a much better cooler anyway, so I'd probably just get that, plus it will come with an AM4 mounting kit. Otherwise, the stock cooler with an R5 3600(x) should perform similarly to a 212 EVO anyway.
I'd probably just hold on to your 250GB 850 EVO since you have, as well as the HDD. No harm in adding more storage though, especially when you can get a 52GB NVMe SSD for 60 quid.
I don't know what you mean by "work effectively"? The 6GB GTX 1060 is a perfectly adequate GPU for 1080p. You will have to lower some settings to get closer to 144FPS in some AAA titles, but you'll easily be able to get 100+FPS comfortably in anything you play. Since you already have the 1060, it makes sense to just use it- unless you can return it and get the full cost back. If E3 comes around and a Navi GPU or maybe Turing GPU interests you, then you can always upgrade the GPU and sell the 1060.