Hey there I just wanted to chime in and say that this build looks great. I actually just ordered nearly the very same list of equipment with a couple exceptions. I ordered a 650w PSU based on the build guide recommendation.
I have not ordered a GPU yet because I'm a little confused about what's appropriate. Most of my usage is Lightroom and Photoshop with a smattering of 4K in FCPX mixed in (but not much, honestly). My Lightroom usage is mostly working with 50+ megapixel RAW files - my working catalog is about 200GB and that's just the *preview* data, not the image files themselves. That's approx 2TB.
On to my questions:
1. I see that you ordered the GIGABYTE GeForce GTX 980Ti 6GB G1 GAMING OC EDITION video card. Is this a good choice for me? Can multiples be used to increase the performance?
2. Can I use the EVGA GeForce GTX 980 Ti 6GB instead? There are two on my local Craigslist going for $300 each so I'll scoop them both up if multiples are worthwhile and they're compatible.
edit: I have an LG 31MU97 running at DCI 4K (4096x2160) if it matters. Every now and then I play games on Steam but it's pretty rare.