Ah, I see. I do tend to assume narrative fiction unless the post specifies otherwise.
For non-fiction things can get ... interesting. Paper-only publication is not so bad, at least you have a fixed layout to target. Technically epub v3 supports a fixed layout variation but that isn't what most people want.
If you have complex layout requirements then, depending on your experience and tastes etc., you may want to learn about
LaTeX. I don't have experience with it myself, but I do know there is a LibreOffice to
LaTeX plugin here.
(The Writer2xhtml plugin on that link is the epub plugin that I use, but you will see there was a 3-year hiatus between releases that did cause some issues, and the "roadmap" says he's removing epub support in the future. He mentions that LibreOffice v6 comes with an epub filter but I haven't tried that one yet.)