[DoctorOhh]

Originally Posted by Tango Mike

I'm using page breaks between chapters so that each one begins on a new page because that seems to be the most common ebook format.

This sounds like a good way of doing things.

Originally Posted by Tango Mike

I've been told not to use multiple hard returns to space chapter headings down from the top of the page or to add space between the chapter heading and the first paragraph of the chapter.

If you use H2 headings then this ought to be easy to accomplish with the bottom margin of the H2 property in CSS.

Originally Posted by Tango Mike

First, with no control over how a reader will choose to view the book, I can't prevent situations in which a few words or lines of text at the end of a chapter appear at the top of the last page, leaving mostly blank space before the beginning of the next chapter. That seems to be something I have to accept if I want to use page breaks between chapters.

This is something you must accept in ePub or Mobi. When using a ereaders two things stand out folks can choose any size font changing the number of screens used to display a page and screens are different sizes on different readers, so controlling widows and orphans is just not the same as with the printed book.

Also there are Forums here for epub and mobi formats that might help.

Good Luck with your book.