I like your decision to use the new option of facing pages with a fold-out. I would not worry about the fact that the student will need to flip back and forth. I have seen many students read with two hands, left hand on the graphic and right hand reading the questions on the next page front underneath. No problem! It is more important that your key face the diagram.
The statement at the top of this page can just as well be formatted as a 3-1 narrative paragraph: "For questions 53-57, refer to the Luminosity and Temperature of Stars diagram below." Follow that paragraph with your notes, key, etc.
I think it is obvious that the questions follow the diagram--I see no reason to explain in a TN.