Re: Longer brake nut: A 30mm nut hits the inside of the front wall of the fork before the head of the nut hits the outside of the back wall (where it should seat). The front brake bolt (definitely not the rear), with sufficient spacers to get the 105 brake pads clear of the fork, doesn't show 6-8 threads inside the fork. I was also concerned about having the bolt extend so far out in front of the fork, potentially increasing the bending force on the bolt.
Re: Sliding on your side to stop: In my experience, the initial coefficient of friction between skin and asphalt is pretty high, but a little blood between the two allows you to slide further.