That is correct. The AUX jack in the car is the 3.5mm port.
That is correct you would have to choose aux in the car to use the nav
The Nav would Cut in because it is using the same Port for the Audio.
You are listening to Google Music (through the Bluetooth / AUX rig i described). and then you need to use google maps to navigate you some where.
Then the google maps navigation would interrupt the Google Music until you were don using it. That inturruption happended on your phone. You did not switch connections in your car (AUX to somethign else)
You are listening to google muisc though the same source on your phone though the Bluetoth / Aux of the car. You get a call. If you have the same phone paired with the car
The car will switch over to the Phone call inturrupting your google music. When you are done wiht the call. The car will flip back to the Aux and your phone will flip back to playing google music.