My name is Diogo Carriço, I'm a pianist and audiovisual artist. I've been using the Leap Motion, also with Ableton, for a couple of years already. In fact, I'm currently developing, with the support of the University of Arts of Amsterdam, a software to use the Leap Motion for musical creation and performance. A tool intended to be very flexible in designing gestures and with that truly feel a connection to what you can do with your synths and effects.
I would love to have a chat with you about all these topics. If you would be interested in that, feel free to write me to firstname.lastname@example.org
But to answer briefly:
Very frequently I use the Leap Motion in combination with a keyboard. Right hand plays the keys, left hand shapes the sound with gestures. Typically these gestures manipulate parameters of the synthesizer and/or of effects after it. I really like to think in terms of what gestures are meaningful to manipulate what sound outcomes, from the performance point of view.
But anything is possible, really. I also manipulate the sound of acoustic instruments, like the piano, trigger new sections of the song, etc etc possibilities are endless. I truly believe in the Leap Motion expressive potential.
The other questions I didn't understand what you or what you are looking for.