The Keystep needs to be manually changed. It has a few modes for how the pattern switches, so you don't have an abrupt jump to the next pattern unless you want that.
Keystep doesn't pass sysex, if you need that, but it sounds as though you won't. It'll pass program changes when in THRU mode and has it's own channel for transposing from an external keyboard, which is different to the one it sends the sequence and arp data on.
You don't need Ableton for anything, but here's the rub, how are you going to send the MIDI from a KMI device to anywhere without a MIDI USB host module, or a computer with a MIDI interface? KMI controllers don't have MIDI din connections which, in my mind, makes them very limited. I really can't understand how a device designed for live performance can be useable on stage when it needs to be tethered to an interface in order to talk to any instrument. Sure it can be run-over by a truck and still work, but what good is that if the PC/USB MIDI host was destroyed by that same truck? I'd have a controller from KMI if they made one with a MIDI din plug or an 1/8th" MIDI out (like the BSP).
That all said, that KMI 12 Step looks like a great controller and hard to pass-by as far as foot controllers go, so grab KMI's "expander" or Kenton's USB host to use it without a laptop and MIDI interface. Even iConnect's MIDI4+ would do the trick albeit be a bit of overkill, but relatively future proof for the stage (large number of MIDI din connections plus a USB host port which is advertised as USB hub friendly).
