What is my question? Where do I need help? Is there a simpler way of doing such conversion JSON --> path/values? How to tell Perl to dive into JSON and find all simple data (scalars...) and return paths and values of them...

I actually think your code is fine. I once showed something related here, with somewhat simpler names for the paths. Also, this is the perfect case for unit tests, so you can be sure it does what you want.