1. Cable management is more down to how determined you are than anything, modular PSU would help massively there too.
2. If it says OEM or Bare Drive etc. then yes you need SATA cables.
3. Doesn't seem like such a big card, i don't see why not.
4. That is more than enough, 500W would easily do it.
5. Depends on a lot of things but with a bit of luck i'd aim for 3.8 - 4Ghz.
6. It can be a pain but once it's done it's done. There are loads of guides around to help you.
7. It should be perfectly playable at ultra high settings, especially at that resolution.
Theres a few other things i wanted to say though, if youre after pure gaming performance then i would go with a cheaper AMD CPU and get a better GPU. I would swap out the 2500k for a Phenom II x4 965 and get a 500W modular PSU. That should save around $80 and you probably wouldn't notice the performance hit in games. For your motherboard i'd get an AM3+ one such as the Gigabyte GA-880GMA (saves another $10) You can then use that cash to get a better GPU, then you will notice the difference. Something like a GTX 560Ti would be great. The GTX 460 is awesome too, they overclock and SLI insanely well. I have the Palit one which is considered budget and i got that from 675Mhz to 900Mhz no problem. (Gets pretty noisy now but only when i'm gaming )
2. Yes an OEM drive doesn't come with SATA cables, but the motherboard usually comes with around 4 SATA cables.
Normally I'd agree with Jmsellars about the mismatch of the CPU and the GPU, but in the case of SC2 it's actually much mroe dependent on the CPU because of all the complex calculations of the AI as well as all the math of hundreds of units all doing damage to each other. Blizzard intentionally gives plenty of leway with the graphics requirements of it's games. an i5-2500k, especially overclocked will perform MUCH better than a 955. More so than a graphics card upgrade would be.
Of course if you are playing other titles then it would probably be appropriate to upgrade. Then again, with the resolution you've stated, the 6790 will more than perform to your liking.