Rivits
something for you to think about
If you release this book through a professional publishing house, all your typesetting and layout work, with defined spacings for titles / paragraphs etc is irrelevant as they will typeset the work using their own house tools.
The less formatting you've got in it, the better
However if you intend to self-publish for the web, then obviously you have to ensure yourself that it looks right. If you've managed that within WP, then simply go straight to PDF - don't add any extra confusion
If you are sending this book to a publisher, as then what format they want. Comments from some of my customers suggest that what publishers often want are double-spaced TEXT files with absolutely no formatting at all. Others like LaTeX. You need to ask the publisher to tell you just what format they need.
If you do need LaTeX, if believe that LibreOffice has an optional filter that strips out the formatting and outputs to that file type, but I've never had to use it. In theory LibreOffice should be able to read a WP file and convert it to LaTeX or most other formats
But - ask your publisher