Had a quick scan. I would break each main-heading into a separate sub-page. On the resultant subpages I would insert subheadings, activities, images etc as needed.
With the smaller pages you will get a feel for tweaking the layout and where to insert activity templates which will enhance the look an feel, but also add pedagogical value. The use of images will also help to balance the pages.
That said - -I did not read the content under each of the sub-headings carefully ;-)