In thinking about my situation, I have an idea as something that may be useful as a PDF extension to the Beginners Box material.
Using only the Beginners Box dungeon mat, iconic character pregens, monsters and materials, a set of four 'Iconic Character' showcase adventures set for one GM and one Level One player. Each adventure is geared to let one GM and one Level One iconic character play through the dungeon mat to completion with a challenging, but reasonable chance of success. Each adventure has unique challenges suitable to the iconic character pregen so the player may understand both that iconic characters strengths and weaknesses.
A useful adaption of each challenge would be to have the puzzles 'randomized', so playing a GM and knowing the solution for one puzzle on an iconic character will not necessarily be useful for solving the puzzle in the same room using the same iconic character.
This is my intended use of the Beginners Box having only my wife and I to fill the roles, trading PC and GM duties where we both wish to understand the game material very well when playing within a group. My wish is that we both know the material well enough we can recruit other 'beginner level' players and have an entertaining game with both of us anchored in the fundamentals without the constant fumbling through the books to understand how things work.
Thank you for considering this request.