Re: startingup with Ableton
you probably don't need any more suggestions so late after your post, but I can't heartily suggest a couple of things...
M-Audio's AXIOM 61 keyboard -- 61 keys (which was a lifesaver after using a 25 key unit for a while). The Axiom has semi-weighted keys which makes a big difference too.
Also, MOTU's Ultra-Lite. I use it a lot for running my monitors, recording vocals and it can also be used in conjunction with a regular DJ mixer as its got 4 stereo outs in the back. Plenty to feed your ableton tracks to a club mixer. Really stable too!
Don't know what mac version you've got, but you may find that you need a little app called "CoolBook" to solve some problems inherent in producing audio with some mac laptops. If you've getting any strange glitches, thats the solution.
peace...