Good call on the PSU, you will need a new one-- the fact that you're unsure about your old on indicates that to me. The Corsair unit you chose will power any single card out there, so if you're not planning to SLI, then that PSU will last you for years. The motherboard you chose does support SLI/CFX, and I'm a big fan of SLI, so I'd recommend having enough power to toss another 570/580 in there on down the line. You could get away with SLI 570s on a 650TX if you kept them at stock, but I would recommend the 750TX or equivalent to be safe. Likewise, you could most likely get away with SLI 580s on a 750TX, but an 850 is always safer.
As far as the CPU cooler goes, if you don't plan to overclock then you don't need an aftermarket setup, but if noise is an issue, you might want a cheap one anyway. Along those lines, if you don't plan on overclocking, then you might as well get the i7 2600 and save a few dollars.
If you want a "top-end gaming machine", then yes. But the way Nvidia designs and prices their cards makes the 480/580 a good value only if you plan to SLI, i.e. truly be at the top end. I say this because 2 GTX 560s/560ti's in SLI will absolutely stomp a single 580, and for about the same price. In fact, 2 GTX 460s will stomp a GTX 580, and for a lot less. So as far as $$$/FPS, the value isn't there in the 580, but if you want the best of the best then it's the only way to go. I guess what I'm trying to say is that I can possibly tell you if the price delta is "worth" the performance delta between two given cards, it depends on how you value your money and your performance.
If noise is an issue for you i would recommend the Asus DirectCUII 560Ti's, they are a little bit more but they are about the quietest 560Ti's around.
They should fit most cases since they are not overly long and the motherboards now general fit SLI just fine as well.