As a prospective customer of the Pocket Reform (PR), I hope that you provoke discussion as to how people use the laptop. Taking your questions in (approximately) reverse order, and excuse me for thinking out loud rather than answering your questions!
Points 2 and 3 suggest that you expect the PR to be docked most of the time at home and want to be satisfied that docking is seamless. Me too: especially since a 7" screen would become rather trying quite fast. One computer I regret getting rid of was an old ThinkPad with a proper dock the whole computer sat in, with all the required ports in the back. Perhaps the modular architecture of the Reform might allow an evolution of this concept in due course?
As for a solution to use Ableton on virtual machine, I suspect that Reform lacks the required grunt. I looked up Ableton on Wikipedia and ended up following links to the creator’s page with side projects. It is a fascinating read!
The Genode / Sculpt operating system (available on Reform) might be an excellent basis for audio tools. I say this as a former BeOS user who remembers how its realtime mixing utilities were mind-blowing back in the day, and unmatched by other platforms. Now BeOS lives again as Haiku, but native radio software Tunetracker was exploring not so long ago to migrate to Genode.
It may even be worth reaching out to Ableton and explaining your predicament. Both MNT and Ableton are Berlin based (and Genode “down the road” in Dresden) so perhaps that might be the spark to make things happen?