Hi @d.a and welcome to the dash community 
There is a new, much easier way to make multi-page Dash apps. This has been in development in dash-labs for a few months and you can find more information here:
The pages/ feature has just been released in dash V2.5.1. There will be an announcement and new documentation available in a few days.
If you would like to get a headstart, I recommend checking out this repo which has a few minimal examples of multi-page apps for dash >=2.51
The multi_page_example1 looks like it might be a match for your project structure. You could try running that app, then modifying it for your content. If you get stuck, then the new docs will be available soon!