Great that you have completed what Google did not do with Android Auto. I will be happy to pay a few Euro for this app when it is released.
I do of course wish that some minor options are are added:
-I often listen to e-books when I drive so I would like the media to be paused when a notification is read.
-Some emails that are read are very long as they contain a huge history backwards in time. For this, I would like to be able to set the reading so that only a maximum of like 20 seconds are read.