1) If you might want to overclock, and overclocking is easy and safe, you need a "K" suffix cpu.
Nothing wrong with a 2600K, but few games use more than two or three cores, so the extra hyperthreads on the 2600K will go largely unused.
The 2500K is 35% cheaper, and will perform the same as the 2600K when overclocked to 4.0.
2) No need for liquid cooling unless you will be looking at record level overclocks. A simple tower type cooler will keep your cpu plenty cool and quiet.
A cm hyper 212 or Xigmatek gais is not expensive. The Noctua NH-D14 is about as good as it gets, and includes some of the best and quietest fans around.
3) 8gb of ram is sufficient for gaming. But, considering the current low cost of ram, I can't argue against 16gb.
I would suggest looking for a single 16gb kit of 4 x 4gb.
Ram is sold in kits for a reason.
Ram from the same vendor and part number can be made up of differing manufacturing components over time.
Some motherboards can be very sensitive to this.
Although, I think the problem has lessened with the newer Intel chipsets. Still,
it is safer to get what you need in one kit.
4) A 1000w psu is overkill. Even a GTX590 only needs a 700w psu.
I am unfamiliar with the quality of compucase.
My short list of quality power supplies would include Seasonic, Corsair, Antec, XFX, and pc p&C.
I might suggest the Seasonic X760w unit. Modular and gold efficiency for less: http://www.amazon.co.uk/Seasonic-X-760-Watt-Power-Suppl...
5) For your budget, and for a gaming pc, consider looking for A GTX590. They are expensive, and in limited availability. But there is nothing better as a single card gaming card. Still, the GTX580 you linked to is a very good one.