Upgrading hardware. Need opinions.

I would NOT spend any money on your current system.

1) better CPU? (rarely a benefit currently in gaming)
2) more than 8GB DDR3/4? (again, rarely needed if you don't have other programs/browsers open when gaming)

3) W10? (main issue is DX12 gaming, but otherwise no rush)

The GRAPHICS card is where you'd gain the most benefit, but you obviously have a new GPU so it seems a shame to upgrade so quickly, especially when properly TWEAKING any game gets you the max or near-max VISUALLY (max may get you 20FPS at 1080p, but visually carefully tweaking can often get 60FPS with not much visual difference in my experience.)

RYZEN?
Ryzen is a little bit of a disappointment, however it probably won't be true in 2018 once we get BIOS, driver patches and better overclocking due to the 4/6-core parts and more mature process load. SMT/hyperthreading is currently buggy on launch probably because Windows is likely running two threads on a single core when splitting demanding threads between two cores would be better (Intel doesn't seem to have this issue anymore so it seems like a Windows driver issue which will be mostly solved in the next few months though it's a big oversight.).

I wouldn't build a RYZEN system (upgrading from your build) unless it gets about the SAME performance in most games but has more cores. Probably a 6C/12T CPU that gets 4.4GHz (ish) clock speeds.

MONITOR?
Don't forget the monitor. If I had that system and a so-so monitor I'd hold off and put money into a GSYNC monitor (2560x1440, IPS, 144Hz) when prices drop a bit more rather than rebuild a pretty good system.

So in ORDER I would:
#1 - GSYNC monitor in 2017/18 (if needed)
#2 - GPU (I'd hold off until 2018 for AMD products to launch though note that GSYNC is tied to NVidia, and Freesync to AMD currently). I'm not saying to buy AMD, just to wait for Vega and prices to stabilize then see what the situation is, especially if DX12/Vulkan may start to benefit AMD more which isn't necessarily as large as some people may think.
#3 - CPU/mobo etc? (last thing I'd do. really a waste of money IMO)

i7-4770k@4.3Ghz -> i7-7700k@5.0Ghz = 20% performance improvement. My personal results. I had a purpose for my i7-4770k, so I didn't mind upgrading to make it available. But really it was a great expense for little benefit.

The 7700k averages about 300Mhz more than the 6700k, I think it is worth it. Which makes sense, pretty much what Intel tacked onto the max boost.

Since you don't have an overclocking motherboard, you could gain some performance by replacing only that and adding 500-600Mhz to your CPU's max boost.

I agree on getting a decent monitor or peripherals. For now you have a decent 1080p machine. Going to the next step is going to cost quite a bit, something like a 1080Ti and a 2K or 4K monitor.

Not really a performance gain going from DDR3 -> DDR4

You can get high end DDR3 3000+ Mhz with lower latencies than DDR4-3000+.

It is your money to spend. If you want to upgrade for the sake of upgrading go for it. I do it all the time.