So a few things, most people have said similar things
No need for an i7, i5 does everything just fine. You can always get an aftermarket fan and overclock it
8GB is only really required, though I guess 16GB isn't too pricey it probably isn't needed
Get a 128GB SSD for the OS. I think it's too expensive to get large SSDs for it to be worth it
The graphics card is good powerwise. I have an ASUS 670 and I can play every game that I have tried in ultra, with only Far Cry 3 taking it below 60fps. The 780 is a bit of a step up than that, so it should keep you going for a little while longer
I don't know about the AMD alternatives though
Also, make sure you spend a decent amount on the power supply and give yourself plenty of headroom either for overclocking or for SLI/Crossfire. Also, get a modular power supply since its easier to put together
I'd also advise going for a case with a window, I love glancing at mine and seeing what I've made







