After a goal or turnover, you must clear the disc. We have two lines on opposite sides of the box 10-20 yards away. We play shorter to minimize running. Also, the defense usually doesn't contest the clear. For more running, you would try to shut down the clear and play 20 yards.
Clearing is determined by first point of contact.
Arguments are permitted and even encouraged. For a goal to count, one of the scored upon players must agree it's a goal. Just because something is illegal in ultimate doesn't mean it's illegal in box. Some people play you can't guard the box unless someone is in it. These people are sissies.