Don't worry about the format too much. As long as you use your sections and Style sets correctly, changing to an appropriate LAYOUT will be easy.
I've used B&N-Press and they have some okay guides and decent service. You can have everything set up and print samples as you make changes.
I do not use Section Breaks as the B&N Press guides recommend. Section Breaks for Front Matter and Back Matter, but use regular Headings (Styles) for any chapter breaks.

While I use WORD for creation, the book cover, with B&N Press, needs to be done as a separate files. You can use InkScape for advanced image work.