I'd suggest to wait around a month or two and get newer components that will make a much better deal for you:
1) For the CPU, Intel's Broadwell-E platform is around the corner, supposed to be released in early June at Computex 2016. The cheapest CPU in this line will be 6800k, and it will feature 6-core die with the price expected to be around 450 USD. Overclock it a bit and you will get a very fast six-core beast. To my judgment, it will be a perfect alternative to the 4-core 6700k.
2) If you decide to go that way, get a decent air cooler. I'd suggest Thermalright True Spirit 140 - I have two of them and they're great. Make sure that you case is wide enough to house such a tall cooler (170mm height).
3) 32GB of RAM is the lowest reasonable minimum for now. In fact, if you plan to use a bunch of apps at the same time (like having Maya, Substance Painter and Unreal Engine 4 loaded at the same time), even 64GB doesn't look so crazy. Though, you can add additional RAM at the later date, if you'll feel that 32GB is not enough for you. As for the RAM speed, it does play some role in overall system performance, but it's not major. Still, I would recommend getting RAM that is a sweet spot in terms of speed and price - don't buy the cheapest and slowest, but at the same time don't pay a lot more for the "extreme" versions.
4) For the GPU - reviews of GTX 1080 were posted yesterday, and it's reported to be around 30% faster than 980 Ti. If the price will be ok for you, custom version of GTX 1080 (not the "reference" Founders Edition reviewed now) will be great buy. It will be faster than a 980 Ti, a lot more energy efficient and will have a 2GB more of video memory (8GB instead of 6GB in 980 Ti) that will play quite nicely for Substance. Budget-wise, GTX 1070 will be even greater in terms of performance/price ratio. It also will feature 8GB of video memory, but will sell for the fraction of GTX 1080's price and it is expected to have a performance close or surpassing 980 Ti. Oh, and you're right - Quadro GPU's aren't recommended for the Susbtance (as far as I know), so a gaming-class videocard will be a better choice.
Alternatively, you can try to look for a cheap Titan X with 12 GB of video memory (maybe the price will come down when GTX 1080 will go on sale). It will not be as effecient, but 4 GB of additional memory may help if you're planning to work on complex assets with 4K textures.
5) Windows 10 works fine.
Hope that helps.