Should I use “Normal” or “Body Text” styles for the text in my books?
For all practical purposes it doesn’t matter; whichever is easier for you. Just make sure you are consistent, and to only apply the formatting that you want to the styles themselves and not to the individual elements in the document, so that you can experiment during the typesetting phase and be sure that everything is updating at once. You could even create your own style if you wanted so that you didn’t have to mess around with the default styles. Just make sure that whatever style you use for chapter headings will automatically go into the style you want text to have for the next paragraph, so that you don’t accidentally mix styles. (Right click on the style and you can edit all the properties of that style including what style comes next, font, spacing, etc.)