What matters here is your budget. How much are you willing to spend on the entire build? That will allow us to optimize a build for you.
You won't need to OC the 2500K much now, but you definitely should in the future. It'll let you do GPU upgrades and keep your system running for quite a while with free OCing performance boosts.
You don't need a sound card unless you have some kind of multi-thousand-dollar audio setup and lossless music files for it to play.
Here's a cheap, decent mobo (ASRock Z68 Extreme3): http://www.newegg.com/Product/Product.aspx?Item=N82E16813157271
I think you should go with 8gb RAM. It's very cheap, and you'll probably need it in the next couple of years.