Org is really good about letting you unobtrusively embed LaTex into a document and can export to a bunch of formats.
I was doing an algorithms course with lots of mathematical formulas last year. Org was a godsend for completing the homework assignments.
It admittedly doesn’t compile to HTML and the compile-time can be on the order of minutes for very large documents, but are these really deal-breakers?
If you really don’t like LaTeX, have a look at org-mode, which seems to be able to fulfil most, if not all, of your requirements (not sure about compile times).