Hi Claire
well, Elijah has already extensively replied to you, so I can only confirm what he said. That is the main reason why I suggested you say "section" instead of "chapter" in your intro/outro.
I would suggest though: record the entire chapter in ONE section and edit and then see how long the final file is. If it is under 74 minutes, it will fit into one section and you don't have to do anything. If it is longer, you could find a natural break in the flow of the story, preferably around the middle, but doesn't have to be exactly half, and cut there. Then you only have to re-record a new intro/outro for both sections.
And then you can insert a new section in the MW if needed. Elijah explained the process in his post.
Sonia