The power supply should be good. The 850w would probably be safer and it's only 20 more dollars. I have a few 6-rx 480 rigs and they all pull between 770 and 820 watts. (all modded) The mV vary from gpu to gpu. Definitely go with the rx 470 or rx 480, even if you can only start out with 2-rx 470/480 instead of 4-rx 460. You will get a better h/s with the 2 compared to the 4 and you can add 2 more in the future.

I would check craigslist, letgo, offerup, etc. for rx 470 or 480 first. I've gotten rx 480 for as low as $100 on there but generally between $130 and $175. This is how I built most of my rigs. Having mismatch brands doesn't matter.

Latest risers iKrazy's link is good also. Mintcell is very good. I've had one 2 or 3 bad ones and they replace them no questions asked.

You need to build/buy some kind of frame. They aren't hard to build. Or you could even buy a two tiered wire storage rack and put the psu and mobo on the bottom and hang the gpus from the top.

I'm working on a video on how to build a mining rig. I'll go through the hardware and how to put it together. Probably should have done a build video like that before the one on modding the gpu. DOH! Hopefully I'll have it up in a week.