I called a Mini Cooper dealer and asked about the key position and they said as long as I don't pull the key out, the steering wheel won't lock (after having turned it on).
However, the power outlets are not powered in the off position so I am thinking of getting an accessory outlet wired so that I will have power when the key is in the off position.
I tested out the Brake Buddy we have today and don't seem to have the pedal problem you described. I have the Advantage model, so maybe the pedal clamp is different than yours? If you would like some photos or copies of the installation guide I have, for comparison, just let me know.
2015 Newmar 3436 LE
2005 Mini Cooper S