Hi,
I can answer just one question, as I have not that much experience in vibe.d

  • Does each Thread have its own Fiber queue so to speak?

Yes fibers are thread-local by default (if there were shared, what would be the point).

Have you programmed asynchronously before ?
If not, please read the paper linked below
http://cs.brown.edu/courses/cs196-5/f12/handouts/async.pdf