Actually, you cannot do dual i7 CPUs in the same PC: They have only one QPI (Quick Path Interconnect), and are thus only uniprocessor capable. Thus, even if the motherboard that you choose did support dual CPUs, you can only use a single i7 CPU on it. You will need two identical dual-processor-capable Xeon CPUs, such as the Xeon E5-26xx models (which have two QPI's), if you want dual-processor-capability. (The E5-16xx series CPUs also use the same socket, but like the i7's are only uniprocessor capable due to their inclusion of only a single QPI.)
In addition, I would get one of the new GTX 10 series GPUs (such as the GTX 1060) these days: The GTX 780 Ti is now outdated and obsolesced, being already two GPU generations old.)
Actually, I typo'd. That should've read "I know you canNOT do dual Core i7's." I'm not that much of a newb, but I couldn't find where to edit posts on this forum. I guess you can't?
Also, I wonder what the price/performance ratio would be of two GTX 780's vs one GTX 980 or 10xx series?
a single gtx 780 ti may be faster than a gtx 980, as the 900 series were optimized for games.
the price to performance would depend on what prices you find for the 780 ti. which card(s) you would need will also depend on how many gpu accelerated fx and lumetri color you plan on using. the newer gtx 1000 series seem to work better with their faster clock speeds and also have more memory.