Ableton Live 8 Users Help?

I have used FL Studio 9 and Reason 5 to produce music, well mess around anyway. So basically I just bought Ableton Live 8 because I heard ProTools9 was for mastering. I am using a Dell Inspiron 15R. Please give me the pro's and con's of using a mac and pc with ableton live. Many music producers I'm interested in (Deadmau5, Skrillex, etc.) use a mac. Also I just bought an M-Audio Axiom 25 25-Key, 2nd Gen. USB MIDI Controller. Do I need an audio interface? I was thinking about the M-Audio Fast Track Pro 4x4 Mobile USB Audio/MIDI Interface with Preamps but I'm not sure what I'd use it for. Someone explain what the audio interface is used for? I have a clue but I'm still learning. What kind of soundcard do you recommend? I am serious about music production. I'm talking about electro/prog house/dubstep. Please let me know what equipment, in your opinion, is decent for making electro/prog house/dubstep.