For what it's worth, a pair of RX 480's will probably be both slower than a single GTX 1070 in most cases, draw twice as much power, and be overall more expensive. I generally recommend that, when people are ready to upgrade, they sell and replace with another single card. I've come to this conclusion after having tried dual GPUs many, many times over the years, from several vendors, going back to SLI Voodoo's in the 1990's.
Regarding CPU choice, I have a few thoughts:
-I would immediately rule out the i5. The i7 7700 + a B250 board is generally cheaper, more power efficient AND faster than an overclocked 7600K. You can run it without issue using Intel's stock heatsink and get a less expensive motherboard, which adds a ton of value.
-Ryzen is brand new and there are a TON of bugs. Bricked motherboards from changing BIOS settings are not uncommon at this point. If you're an early adopter, you can basically expect problems. Intel's lineup is very mature and largely problem-free.
-Why not consider the i7 7700 or 7700K, which are basically the same price as the 6xxx CPUs, only faster?
-Intel's i7's win in basically every benchmark against AMD's Ryzen CPUs in games, most likely because even though gaming is becoming more threaded, and 8-thread CPUs (Core i7) show real benefits over 4-thread CPUs (Core i5) in recent games, per-core speed is still very important and Intel's chips are both faster per clock and clocked higher than Ryzen. However, Ryzen is still very respectable and within spitting distance of Intel's offerings, while offering much better performance in things like encoding and rendering, due to having twice as many real cores.
-Ryzen is more power hungry and you can expect it to dump more heat into your case/room, but this is in part because you're getting twice as many (if slightly slower) cores.
I don't think there's a wrong choice between Ryzen and an i7. If I could choose which were to be given to me right now, I'd probably pick Ryzen because I enjoy tinkering with new stuff. More cores is probably more future proof, too, but you can expect to have a far more trouble-free experience and better performance in today's games with an i7.