I've got Blackvue cameras in all my cars including my Z4. I initially had the rear camera on the wind deflector but I recently got a piece of clear plastic that I custom cut to fit inside the driver's side roll hoop so it's not just stuck out in the open looking ugly. (I'll get a pic shortly and edit it in to this reply)
As for the fuse; I can't remember the exact ones I tapped into with the add-a-fuse but I just checked with a test light for one that was only on when the ignition was on, and one that stayed on even after the car went to sleep. That was for a Power Magic Pro though, I think you'll just need to find one that's on with ignition only which makes it much simpler.
Pic of the rear cam installation:
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