1. In the menu, vehicle settings, park assist. Change the alert volume (page 303 of the manual). I don't think it turns the radio down but I've never found the beeps are drowned out.
2. As above, in the menu you can adjust the voice volume. Page 409 in the version of the handbook I have.
3. Don't leave it on auto when parking up, especially in winter conditions. If the blades are frozen it can activate when you start the car and damage the motor/blow the fuse. Treat it like auto intermittent speed, not something to leave on even when it is dry.