I'm learning Ableton Live, and I need a MIDI controller.

Playing drum machines and samples live with a band, just like NIN.

Technically I already have a Casio CTK3000 which has MIDI.

Do I need a controller/mixer?

I've narrowed it down between a Launchpad+Mixer and an APC40.

The AKAI is a bit too expensive for just starting out, but I've decided that I want to buy quality equipment to last years, not continually buy stuff.

And what's up with them not supporting open source stuff?
I personally run 2 keyboards and an Akai mpd pro 24 to a computer live to trigger samples and play synths live. I have a pretty good setup but not a fan of albeton so can't help you to much.

But you shouldn't need a mixer if using midi. But you will need an interface to use a good line out.