Hi,
I have a new book available on Blender Market and Smashwords that digs a bit deeper into all sort of practical issues that are not so straight forward to solve when developing Blender add-ons.
It is called ‘Blender Add-on Cookbook’ and based on all sorts of issues I encountered when developing free and commercial add-ons in the last couple of years.
It is a fair bit more advanced than the book Creating Add-ons for Blender so you should have some experience in developing Blender add-ons already but both sites offer a sample of the book to check out if it is something for you.
Regards,
– Michel.