Yes, I'm a noob...

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Do plan to go with the Mixtrack but what would be a decent soundcard? I've read everything from a 2.50 usb part to a Behringer UCA222 to a Traktor Audio 2?

When I used an NI soundcard, I had a hell of a time with it and never actually got it to work. I think the one I had was an audio2dj which was the precursor to the traktor audio 2. Maybe the traktor 2 would be better and wouldn't be as glitchy as it's precursor. Otherwise, I recommend the Numark DJio which they just revamped and made alot better http://www.numark.com/djio
 
As a beginner I would highly recommend you go with the mixtrack pro. High quality built in sound card and no hassle. Buying an external soundcard can save you a tad bit of money but it wont come without it's hassles... just my thoughts. Because I own a mixtrack pro I can't help you on choosing a soundcard, but I can say I'm very happy with the built in one.