At this point it would be a total waste of money to get a GTX 1080 'cos not a single program even supports it and most likely even the upcoming CC 2016 versions won't in their initial releases. That aside AE's use of GPU acceleration is limited as it always has been and even in Premiere Pro you may not see much of a difference between cheaper GPUs and more expensive ones since you may never actually get to a point where that would be necessary. At least in the graphics department this is seriously over-specced. You could easily get a GTX 970 and save almost 700 bucks on that alone. The rest will depend. More expensive motherboards simply tend to have more controllers like additional USB 3 ports, onboard hardware RAID or even an extra full PCIx lane for additional graphics cards, most of which you will quite likely never use, anyway. More memory on the other hand never hurts, so definitely get 32 GB. Everything else we can't realyl know. A lot of pricing differences come down to where a vendor gets his stuff. Large outlets often use bulk ware directly from the manufacturers and their supply chains and due to mass get huge discounts whereas local retailers usually depend on using nicely packaged retail versions which are more expensive to begin with.
Thanks for the reply! That is very helpful info, I think I'll stick to the older cards as you mentioned then and upgrade later when everything seems to work nicely with them!