Welcome to Xoutpost, Holger! That really is a beautiful E53 you have, thanks for sharing the pix.
I'm particularly interested to hear about the progress of your RPi project. I would like to get one set up in my E53 as an audio player. I intend to keep the original MID/CD player, using the RPi through the Aux input. Maybe eventually completely integrate the RPi as a replacement head unit. Let us know how your project goes.
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2003 E53 3.0i
DOB 10/15/2002
Sienna red, Savannah Beige Dakota leather
Type FA53, Engine M54B30
2018 G02 30i
DOB 4/21/18
Black Sapphire Metallic / Canberra Beige Vermasca leather
Engine B46O