notice the custom part box accounts for two more GPUs, I'm not sure why the site doesn't let you add 4 to the GPU section.
This setup ranges from $5250 with 4 GPU to $3240 with 1 GPU. You might want to bump up the PSU for 4 GPU its currently 1500 watts, which may or may not be enough at max load. The article shows a max of ~2800 watts with 8 GPUs
Mobo does not support 4x16 PCIe lanes (that's why they didn't want you to add 4 GPU cards).
Mobo is limited to 64GB RAM.
$520 for two 256GB 840 Pro SSDs? Seriously?
Here's a better mobo: https://www.amazon.com/Motherboards-X99-E-WS-USB-3-1/dp/B00X...
Also, you can literally double the RAM for the same money: http://www.ebay.com/itm/128gb-DDR4-8-Crucial-16gb-DDR4-2400m... (keep in mind that speed of RAM is irrelevant for DL tasks).
The server we sell is packaged with software we wrote that makes administering significantly easier. We also provide technical support and even a limited amount of free machine learning consulting. The customers who purchase this server want a headache free solution and aren't as price sensitive as a lone researcher.