the i5 that i included in the build cannot be overclocked..but cpus like i5 3570k can be overclocked and require a custom cooler.
and no need for a sound card as the motherboard comes with an integrated sound card..
I noticed you didn't include a sound card or cooler. That's not necessary? (Sorry, don't know a lot about computers)
There is already a chipset on the motherboard for sound, comes with all modern motherboards, sound cards are only needed if you are making serious music, or if you just want a vibrant experience when playing games.