I'll reply on the other points tomorrow, but for now:
...AFAIK, OpenType allows different variants of a font in one font file
(ex. normal and bold). We've had requests to support those font files.
Have you found out during your investigations what would be involved in
supporting this and would this be in scope for your work?...
AFAIK, several OpenType fonts can be packaged in a single file as
"TrueType Collections" with a .TTC file extension. If that's what
you're thinking about, extracting the individual fonts from such a
file shouldn't be a problem.