The only major problem is you have picked SO-DIMM RAM, which is laptop class RAM (204 pin). You need desktop class RAM (240 pin).
970s seem to be OK, but are still in the testing phase since the release of Yosemite. I suggest you keep an eye on the forum to check its progress. Only those GPUs listed in the Buyer's Guide are 100% supported using the methods outlined on this site.
If you are after 780ti based performance, perhaps the 980 would be a better option? I typically recommend 1 higher performance GPU, in lieu of 2 lower performing GPUs in SLI.
Maxwell refers to the name of the chipset used in the GPU. As I understand it, the 750ti was the first Maxwell based GPU from Nvidia. The new 970 and 980 both use the Maxwell chipset. Since support for Maxwell in Mavericks did not exist (i.e. they were not used in Apple based products), they were not supported as GPUs. Support seems to be there in Yosemite though.
Couple of suggestions:
1/ What are you primarily going to be using the computer to do? Is it worth upgrading to the i7 4790K? The rest of the build is pretty high-end so this would make sense, especially if you are into video editing.
2/ I would seriously recommend an SSD, as well as the HDD. They provide the most obvious performance improvement in my opinion and are worth the extra price. I personally use 2 x 250gb SSDs (1 for OSX and 1 for Windows) and have a 2TB HDD for additional storage.
Hope this helps