Help with gaming build

[Elusive]

Hey everyone,
I've been looking at building a new gaming PC as mine is getting a bit outdated (Q6600/GTX285).
I've been thinking about getting:

• i5-2500K
• GTX580
• 8Gb 1600MHz RAM
• A basic Z68 Mobo

This isn't my first build, but it's been a while. I have a few questions surrounding this.
Firstly, what sort of power draw would this have ie. what wattage PSU should I get?
Secondly, I'd probably overclock the CPU, but not to the extreme; is the stock cooler fine or should I consider something like the Gelid Tranquillo (I've read good reviews for a cheap cooler)?
Thirdly, how future-proof do you think this build would be? I've had my PC for about 4 years, and would like that to be the case again.

Thanks in advance

 

[Elusive]

Thanks for the swift and accurate reply.
I've also seen people talk about getting 6870's in crossfire as an alternative to the GTX580.
Back when I built this PC crossfire was generally a terrible idea due to lack of support/drivers and terrible performance; what is it like now?