It sounds like you do not yet know about
Bodsy's Brake Bible.
Below are links on disco3 to Bodsy’s Brake Bible, a free 36 page pdf containing all you need to know about all three brake "systems" on the 3.
http://www.disco3.co.uk/gallery/thumbnails.php?album=4184
Download the latest version; v1.6a. As of when I last looked, there has been over 17,000 views/downloads of his free 36 page pdf. I see he now has a French edition as well.
The black art part is probably towards the end, (page 27/36 and following), re the electronic parking brake.
Rather than perhaps black art stuff, it may better be called leading edge, or maybe bleeding); also the
set and unset procedure applies when doing just a normal rear pad change.
If you ignore the set unset procedure, then a few miles down the road, the squealing will almost assuredly start.
The good news is the fronts are more normal, but the rears, not so!
In total, for the vehicle, you actually have three pair of brake assemblies to deal with: (1), the front pair of rotors, and pads, (2), the rear pair of rotors and pads, and then (3), the parking brake pair of drums and shoes – yes, drums and shoes sitting behind/inside the rear rotors.
That is why you can use the parking brake as a “dynamic” system to safely slow the vehicle from highway speeds. The owner’s handbook explains the procedure as below.
Dynamic operation: In an emergency, the park brake can be applied dynamically: i.e. with the vehicle travelling at more than 3 km/h (2 mph). Pulling up on the lever and holding it up gives a gradual reduction in speed. The brake warning indicator will illuminate accompanied by a harsh sound and “
Caution! Parkbrake applied” appears on the message screen.
The stop lamps also will illuminate. Releasing or depressing the lever will cancel the parkbrake application.