I think you gave me the answers:
0) It seems reasonable to just use sphinx,
no jekyll or anything more, only if a need for it is found.
I might use some HTML generated by vimwiki for pure convenience.
1) Make the main documentation with sphinx.
That means joining:
<githubio sphinx music>
, gitbook, readthedocs, all is just as fine.
makes it easier and has more features,
while readthedocs is maybe more traditional for these kinds
of python-related docs.
3) just realese on pypi, make the documentation fine
and tell the list. If any major release deserves a message,
it is ok to send.
3.1) A scikit to make psychoacoutic experiments, synthesize audio and music,
is not absurd nor deeply compelling.
4) Am I loosing something? Being mindful of this question is always good, but that is it,
we are on track.
(the python and latex files are on github, so there is an issue tracker,
a wiki etc etc there if anything comes up)