1. Not sure if this is a trick question because it seems pretty straight forward. But at the risk of being duped, I'll give the obvious answer of the B-10. It's the first "big" yard line from the back stake.
2. I've heard arguments both ways, but I put it on 4 as just a little reminder that the 4th down fumble rule applies. The leader of H breakout session at the TASO who I believe is a Big 12 H agreed, so I feel pretty comfortable with that.
I'm not sure what you mean by "what does it do?".