I'm not finding much about what data I'm sharing and what data stays with the Head Unit Basically I want to minimize it since I'm (currently) only looking to run google maps.
Stuart made a reccomendation to use a different Google account but it's not clear how to set that new account as the one used by Android Auto.
I am certainly no expert, having not used Android Auto before. But as I think I understand, all data stays on your phone, it is not seen by the head unit, which is basically just acting as an external display for your phone. So of course your Android phone would be using the Google ID you have on your phone.
I believe what Saab Unleashed means by having a "burner Google account" is for when not using Android Auto, but using the head unit as a stand-alone Android device. In this case to use Google Play or Youtube or Maps on the device (again NOT using Android Auto to link to your phone), do not login to Google on the head unit with your "personal / real" Google account, instead use this "burner account".