Firstly, I thought it would be good for consistency to include the objects on the front cover as part of the artwork of the piece. Initial experiments on the scale of the image:
I think 75% provides a happy medium of 50% and 100% scale. 50% is a little too small, the composition looks a little lacking at the top and the bottom of the image. 100% doesn't contain as many objects.
A mock up of the PROOF emboss effect that would be consistent with the yearbook. I think it would be best to only include this as part of the front, as the image is already complex enough.
The view from the other side.
This is the page as it stands in the yearbook. When copied directly to an A5 scale this is what happens:
On a different format, there will be some type that needs to be moved around. A5 is exactly the same width as the book, but has a slightly smaller height.