How do I trigger a scene in Ableton?
Re: How to trigger next scene with *one* click via MIDI? Then, under Preferences turn on "select next scene on launch". Now, when you hit the key/button on your midi controller it will launch the currently selected scene AND automatically select the scene below it. This is what you need.
How do I play all scenes in Ableton?
Select all the tracks at the top from left to right and press Ctrl+G to group them. This creates a group of all the selected tracks and now you can setup a follow action to play the next scene for each scene on the grouped tracks.