1st build

Hey there guys. So i'm looking to do massive pc build in the next few months and i very keen on using unraid to really take it to the next level. How ever i have done a  fair bit odf reading up and i still have a few questions which i need to have answered before i commit the the build with unraid.

So first of here is what i have planned hardware wise:

CPU: i7-5930k

Motherboard: Asus x99 delux/USB 3.1

RAM: Corsair Dominator 32gb (4x8) 3200

Hard Drives: 2x Corsair Force LE 240GB 2.5" Solid State Drive (one for each of the two vms i plan to run)

                    Samsung 950 PRO 256GB M.2-2280 Solid State Drive  (for the cache)

                    Western Digital Black 6TB 3.5" 7200RPM Internal Hard Drive (for the parity drive)

                    Western Digital Black 5TB 3.5" 7200RPM Internal Hard Drive x3 for the storage array

Gpu: 3 xMSI Radeon R9 Fury X 4GB Video Card

PSU: Corsair AX1500i 1500W 80+ Titanium Certified Fully-Modular ATX Power Supply

Case: Corsair 900d

Now with this build these are the goals i am aiming to achive with it.

With all the hard drives i essentially want to set up an expandable nas storage system, its also why i chose x99 chipset as they tend to have more sata connections (as well as the fact x99 has more pcie lanes for multi gpu configs) to allow more drives to be added in the future.

Then i will be running two gaming vms. 2x r9 fury will be used to power a 3440 x 1440 screen and the other r9 will be used to power a standard 1080p gaming rig.

Now my questions at this point are how the gpus will work. I  have heard that nvidea sli doesnt work with unraid but cross fire does hence why i have chosen to go with r9 furys. However i hear that you need to dedicate a gpu to unraid when setting it up. Will i be able to pass through 2 of my r9's to my primary vm and still have the other pass through to the second vm?

Also how will installing games work, Will just need to install them to the array hdd's and then both vms can access it or will they need to be installed to the vm ssd's?

And how does 2 vms hold up with online gaming, Lets say both vms are playing an online game like sc2 or dota, will there be a noticable difference for the internet? (for reference my internet is 200/20)

For any questions regarding cooling all these components i am plannig to do a full custom water cool loop to go with it. Ill add more questions as i think of them but so far my only real concern is how gpu pass through will work on the x99 chipset with no igpu on the processor to use in place of a gpu card for setting up unraid.