Thanks for the questions. We can't answer them fully, because some issues are a part of the competition task and the answers should be found by participants.
1. We confirm that there are 5 nodes which are connected with itself. It is a bug in the OpenStreetMap data.
2a. Sure, otherwise there would be no jams
3. See the task description
4. It's close to the real-world model of traffic.
5. The average speed is a harmonic average of velocities of all vehicles that entered the segment within that 6 minute period.