Yes. The cross-bar may not be substituted by a rope in order to finish the match.
No, such flags are optional.
Dotted or broken lines are not in accordance with Law I and must therefore not be used for marking the field of play.
Yes, if it is marked outside the field of play, at right angles and at a specific distance from the goal-line and touch-line respectively and at 9.15 m (10 yards) from the edge of the quarter circle.
If the referee notices this being done during the match, he need not interrupt the game just to caution the player who is making unauthorised marks on the field of play after the match has been started. The player concerned must be cautioned fur ungentlemanly conduct when there is an interruption in the game. If however the referee notices this before the match starts, then he shall caution the offending player immediately.
Yes. The Law implies it is optional, but it is advisable to attach nets, since a National Association or a competition may enforce it.
No.