The HAF 912 lacks front USB3 ports. If you don't want the Redbone, try the Challenger:
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Sapphire isn't the only company to make a 7850, but getting the 2GB is a decent idea if you don't mind spending the extra money: »www.newegg.com/Product/ProductLi ··· eSize=20
PSUs aren't scary at all if you go methodically and read what goes to what, but modular PSUs are great ideas because you can remove the un-needed cables and the inside of the case looks a little neater. The Corsair you listed is fine.
The motherboard comes with SATA cables (it comes with two) and the PSU comes with power cables. It might not hurt to pick up one or two more SATA cables.
If you have never worked on computers before, grab
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(never know when you may need to re-mount your CPU cooler)--
Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety.