I have the 500r and used the standoffs that came with it. Those are just holes that look like standoffs. Use the ones provided and put them in order that corresponds to your motherboard.
You will find a good deal on CPU and Motherboard. I'd pick this up from microcenter:
i5-3570k $190 + tax
Gigabyte GA-Z77X-UD3H $100 + tax.
Still comes out a lot cheaper than buying those two parts from newegg.
You need 40A on the 12V rail to run a GTX 580. The Neo ECO 520W has 40A on the 12v rail. IMHO, that is cutting it way too close to be worth it. I'd also feel a lot safer with 600W.
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GeForce GTX 580 review
By: Hilbert Hagedoorn Edited by Ian R Barling | Published: November 9, 2010
Hardware installation
Installation of any of the GeForce GTX 580 card is really easy. Once the card is installed and seated into the PC...
I'd rather get:
AMD Phenom II X4 965 BE $110
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103727
and
AMD Sapphire Radeon 7850 $240
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102998