In your 1st picture (the top one) what is going on at the end of the rope? (right side of the picture)

Is that just a knot to prevent the prussic knot from sliding off?

Finally, what type/size rope do you use? I currently have a soft nylon rope, picked for its suppleness, but I am a bit concerned with the 'stretch' that it has, is a stiffer rope preferred even though it doesn't move as well?