1) UTF-16 is like UTF-8 except
it takes up more space. On the theory that if you use a lot of Chinese/Japanese characters it will actually come out to less space.
Seriously, just use UTF-8
2) Correct.
3&4) The only rule is that the mimetype file must be first, and uncompressed.
You can use e.g. advzip after-the-fact to recompress it with zopfli for space-saving -- advzip will NOT try to compress the mimetype, since its a) too small, and b) it doesn't recompress file that were stored without ANY compression.
Whatever other program you heard of probably did more or less the same thing, but with a particular affiliation of brand loyalty.
5) calibre's editor. Or else Sigil, but I am more fond of calibre. They do all the paperwork for you.
Failing that, it's simple with zip.exe -- the appropriate incantations are:
Code:
# Add mimetype without compression.
zip.exe -X0 C:\path\to\ebook.epub mimetype
# Add all files other than mimetype and platform-specific crap,
# using zip's maximum compression settings.
zip.exe -rDX9 C:\path\to\ebook.epub * -x "thumbs.db" -x mimetype