I am not sure what is the main question? I am sure search of the forum will give many insights and Getting Started on /e/OS.
For “Fully degoogling” I am afraid that you may now have to search for a degoogled car. Many cars have an Android head but worse they have some “transfer box” deeper down also run by Google. (I read that car manufacturers can get free support from Google to include Google proprietary software.) [1]
Currently (in current standard search, @Manoj) of Support topics the page is not found for AA but threads with hastag android-auto discuss the subject.
[1] The initial proposal to car manufacturers is seen Android for Cars | Google for Developers