Ok, here's an example of how I plan out a 2-page spread, for my new book, Worldview.
I quickly sketch out the content, adding dummy text boxes and insets to form a rough composition. Once adequate, I add the image to my other drafts so as to return at a later date. On returning, I can fully render the sketches, fill in the relevant text, and shift elements about, baring in mind safe zone margins, crops and the centre line of the 2 pages. For now, this is adequate for my needs.
FB Worldview Page - https://www.facebook.com/WorldviewBook/