As far as your other build, there are numerous compatability issues.
1) You chose LGA 1155(pins) CPUs with an X79 motherboard that only supports LGA 2011(pins)
2)You can only SLI/Crossfire identical cards. They don't have to be from the same partner, but they have to be using the EXACT same GPU chip, modified to identical settings. 7950 & 7950 for example is possible. Asus 7950 and MSI 7950 is also possible, even though they are not manufactured by the same partner. However 7950 and 670 won't work together.
Yes, but your using the older Z68 motheboards, for the older 2nd Gen i3/i5/i7 Sandy Bridge CPUs. You wanna get a newer Z77 board optimized for the newer Ivy Bridge CPUs. My builds are very solid, I think most people would recommend them.
Well for one your possible build would look funky blue mobo red led case fans last years top notch stuff pretty much so all i really did was take from the current parts you were considering and throw together the current what's best of those and i made sure ram was blue case leds blue mobo blue and the new ASUS P8Z68-V PRO is this in this build and the PSU i picked you is better bang for your buck with a seven year warranty and the hard drive is also just as good as well as cheaper than your pick anyway hope it helps PCPartPicker part list / Price breakdown by merchant / Benchmarks