Wordpress plugin development

General information for the website: car repair
Kind of development: Customization of existing website
Num. of web pages/modules: 1
Description of requirements/features: Wordpress is already installed on my website, there is some articles and multiple level of category created.

But I need have a page which people can navigate in the subcategory and access to article of the last category(s) selected.
I have one general category called " voiture" which shouldn't be show, under this one there is multiple level of subcategory.
Each time I select a subcategory, I want to see the next subcategory of this one and articles (title and extract) of the selected category and article of the level up category ( except if category is "voiture").

To show these categories I need dropdown list or something similar.
It could have many categories in each level it must stay friendly to use.

You will find below an approximate picture of what it could look like.
If you find a better design, enjoy but first I need like the functionnality.

The code must be comment and be the lightest possible to keep performance.
Extra notes: