We will probably use an Adafruit Sound Board to store and replay the audio bits.  The board is very small and it can handle multiple audio files. We're looking for larger blank board books (about 8" x 10") and membrane switches.

Technical challenges involve sizing the book, creating an electronics enclosure and making photos and text adhere to the board material.

To create finished books for other people, it will be necessary to find songs and produce audio tracks that are royalty free--so that's an intellectual property challenge.