TBH I don’t remember if it was wired or wireless but my understanding is that GrapheneOS’s implementation is essentially the same as what is included on stock android for Pixels, so both wired and wireless work (https://grapheneos.org/usage#android-auto).

I used it with a stock system so not aftermarket. Do you have any specific reason to believe aftermarket systems wouldn’t work? If they support android auto you should be fine.

Yes

https://privsec.dev/posts/android/banking-applications-compatibility-with-grapheneos/

If I can answer any questions about GrapheneOS lmk. Android auto works, I don’t drive much but I’ve used it before. You can also ask on https://discuss.grapheneos.org/

/e/ OS is not more secure than lineage. It tends to lag behind on security updates by months.

https://eylenburg.github.io/android_comparison.htm

For privacy, security, and usability, GrapheneOS is the best alternative mobile os by far. The only downsides are if you don’t like or can’t afford Pixel phones, and even GrapheneOS won’t have certain features you may need such as mobile device management, google wallet nfc payments, certain apps especially banking apps.