Actually the constellation es is more reliable and a bit faster than the barracuda, the enterprises hdd are reliable and they're expensive, so the hdd is fine.
It doesn't include the os, the op needs one.
The club3d 7870 joker card is a tahiti le, i wouldn't change for a standard 7870 like the asus. http://www.overclock3d.net/reviews/gpu_displays/club_3d...
@op, your the build is good, the 7870 le will maxout skyrim.