Yes, all of those things you mentioned are actually quite easy. Have you looked at Follow Actions yet?
Follow actions work on clips, not scenes. As far as I know, there is no direct way to trigger a particular scene at a particular time, though I imagine it can be done with Max for Live or ClyphX.
And before you try to tell me that I can achieve the same effect as triggering a scene by triggering each clip in the scene, allow me to point out that triggering a scene can change the tempo and/or time signature.