1). Personally I'd recommend a GTX 1070 or 1080 if you're going to be spending a lot of time in 4k, especially double 4k monitors.
The GTX 1060 only has 6gb of VRAM, and no SLI support (technically). It's generally regarded as a top-of-the-line 1080p card, but a stretch for 1440p, and a real stretch for 4k.
2). The two network cards are usually not necessary, but you might be running some stuff we're not familiar with so props if you are.
3). This PSU isn't that bad in my opinion, but it's sort of low on the "PSU reliability hierarchy".
Good luck man, you have a good build. Make sure that once you get your graphics card to verify which monitors will be running displayport and which will run HDMI.