I want to bring into Live performances sounds that we used on the album. These were from other sources than the M3 (guitars, vocals, other synths, etc). The only piece of gear on stage will be the M3. No laptops, no instruments or anything else. Don't ask why!

So far so good, but the singer sometimes requires tempo changes during the performance, according to his or the audience's mood. Not more than +/-10 BPM though. So that's my problem - I don't know how to seamlessly achieve this. I don't own the M3 yet.
Questions:
1) How will the audio samples react to real time tempo changes? Will they automatically stretch/shrink to stay in-sync with the other MIDI Tracks?
2) But if I slice them (based on their attack) prior to importing them into the SEQ (hence I bring only the slices to the sequencer) - is this a better approach?
3) How many tracks in the Sequencer can contain MIDI Notes that trigger samples? Is this limited?
4) It reads that M3 has 4 Inputs. Can I record 4 external sources of audio simultaneously? Let's say on 4 different tracks?
5) How can I adjust the volume of the tracks that contain samples relative to the other Midi tracks? Will the volume slider of the track also affect the loudness of the audio samples?
Any feedback will be appreciated.
Thanks.