I personally wouldn't go with Ryzen at this point for a predominantly gaming build.
The 8th Generation intel processors are due on Thursday (5th of October). The 8700k is a 6 core, 12 thread cpu and from the leaked reviews seems to clock near 5ghz. Intel official specs
Intel® Core™ i7-8700K Processor (12M Cache, up to 4.70 GHz) Product Specifications
8600k is also one to consider as it'll be cheaper and clock higher (by all accounts) although you lose 6 threads (6core/6thread as opposed to 12 on the i7)
For gaming (and now even multi-tasking) the 8th gen intel is going to be pretty strong.
Even if you decide not to go with Intel, there's pretty strong rumours of a price drop on Ryzen. Anyway you're not buying immediately so at least you'll have a clearer idea in a months time what the landscape is looking like.
There'll be hands on user reports of the 8600k and 8700k and prices on Ryzen will have settled.
I appreciate Ryzen 7 has additional cores, but for gaming 6 is more than enough. I'd apply that same logic if you're adamant on going with AMD, i.e be looking at a 1600 and spending more on the gpu if you do go with Ryzen.
Just to add, I'd also save some money on the motherboard too. With Ryzen cpus not being great overclockers, buying a high end board makes little sense. I'd probably look at a b350 board, or a lower x370 (if there are features you need on that chipset).
In a gaming build at higher resolutions, the graphics card is what makes the biggest difference. Put it this way, at 1440p you'd get a nicer experience with a 1600 and 1080 than 1700 and 1070.
If I were you (and adamant on Ryzen) I'd probably go for a 1600, a micro atx b350, and with the savings made on the motherboard, the smaller case, and cpu I'd be buying a better gpu.
But ultimately I'd be going for an i5 8600k which will likely be priced around the same as the 1700 and I'd bet my life that it performs better in gaming, let's face it the 7700k is already stronger in gaming....
The only thing I would say is, I don't want the CPU changed, it will be overclocked.
I'm curious why you don't want to change the cpu?
What are peoples thoughts on the motherboard? It seems to get good reviews, but I haven't really had much time to do a thorough check to see if theirs anything out their much better?
The 3 "best" x370 motherboards are the CH6 (crosshair hero), Taichi(AsRock) and the Gigabyte K7. The CH6 is very well regarded so you can't really go wrong, but again I'd go back to the fact that Ryzen cpus just don't overclock that well so most ryzen owners are getting similar overclocks on lower end boards. I think with Ryzen, choosing a motherboard really comes down to features, aesthetics, and ram compatibilty as some boards are finicky.
With regards to the ram go for these (save 86 quid too compared to the ones you picked). Developed specifically for Ryzen, they use Samsung dies, which is what you want. Although a giveaway is most CL14 ram tends to use Samsung.
https://www.amazon.co.uk/gp/product/B06XFT7DF9/ref=ox_sc_act_title_7?smid=A3P5ROKL5A1OLE&psc=1
With a saving on the ram, the cpu (1600) and motherboard (b350) and case you'd save nearly 300 quid which puts you near 1080ti money