Again, you want your digital page to look as much like a printed page as possible and most printed books don't have additional white space between paragraphs. (madgeniusclub.com)
Most print books use full - justified text, so that the right side of the text is lined up along the right margin. (authorhelp.uk)
For most print books, you'll need an ISBN from somewhere in order to get into libraries or bookstores. (deirdre.net)