Some further thoughts for you while you consider the video editing question:-
CPU: Intel Core i7 6700K - Good - I'd love one but can't afford it (I've ordered an i5 6600K)
M.2 Super-fast SSD: Samsung SM951 512GB NVMe - Good - I'd love one of these too - I'm hoping they'll get cheaper
Hard Drive (data): 3TB S-ATAIII 6.0Gb/s - Fine
Optical Drive: 10x Blu-Ray RW S-ATA - Fine
Sound Card: Onboard 7.1 Audio - Fine unless you're an audiophile in which case you would probably want something better.
Case: Corsair Carbide Spec-01 - Fine (can take motherboards upto ATX if required - although see CPU cooler comments.)
Monitors: Iiyama GB2888UHSU-B1 4K LCD ( HDMI, DisplayPort, VGA) - Fine - Display Port will be the connector of choice (4K is not on my horizon yet).
CPU Cooler: Stick with an air cooler if your not planning to overclock - CoolerMaster Hyper 212 Evo seems a bit too high for your case at 159mm (by only 9mm so MIGHT fit) - TX3 Evo should do the job. Or consider a slighly larger case.
Motherboard: Gigabyte Z170MX-Gaming 5 - This is a micro ATX board that you're planning to put in an ATX case - so I.m not sure what you're gaining here over say an GA-Z170X-UD3 board which is ATX size. You do get slightly better audio facilities on the Gaming 5, and the alloy strengtheners around the PCIe x16 slots - but it is a bit less expandable & somewhat more cramped & more expensive by about £20. I also prefer to have the Intel LAN chip fitted to the UD3 (so guess which one I've got on order).
RAM: 32GB Corsair 3200mhz Vengeance LPX DDR4 (4x8GB) - Good - although you don't need this speed if you're not overclocking & could possibly save a little by getting slower speed RAM. Personally I've not had much luck with Corsair although most people seem to think it's excellent stuff.
Operating System: As I've already said I'd use Windows 10 x64 Pro (this year's PC deserves this year's operating system, 7 is fiddly to install & there's no reason to consider 8 in preference to 10)
Keyboards and Mice: Logitech MK270 Wireless keyboard and mouse - as far as I can tell the MK270 does not have the Logitech Unifying receiver, and the mouse & keyboard supplied are not unifying compatible. So if anything breaks, particularly the receiver, you may have a problem. Consider the K270 keyboard which is unifying compatible & comes with a unifying receiver then get the unifying compatible mouse of your choice. Then you can run both keyboard & mouse on the one receiver but have individually replaceable parts when something breaks (and have a spare receiver already available). My preferred mouse is the M510.
To be Established
Graphics card: 2 x NVIDIA GeForce GTX 980 Ti 6GB - depends on video editing software
PSU: 650W Corsair RMx Fully Modular - depends on graphics card(s)