Hard to give an exact length for Rage's story. It could be short and to the point or long and filled with twists and turns. A lot depends on how much background, character development, and events are included.
One possible reason could be that Videl does something that endangers herself. Gohan, being protective, might get angry out of fear for her safety. For example, if she recklessly jumps into a fight without proper training or preparation.
However, it could also be a turning point. If Gohan realizes that his anger is misdirected or if he communicates his reasons for being angry to Videl, it could strengthen their relationship. They could learn more about each other's boundaries and grow closer as a result.
No. Ken's rage might be just one aspect of the story. There could be other characters' emotions, motives, and events that are not related to his rage but are essential parts of the full story.
Yes. If the story is a character study specifically focused on Ken and his rage is the driving force behind all the events and character development in the story, then it can cover the full story.
Gohan's story seemingly ends when he realizes that a peaceful life is more important for him and his loved ones. He steps away from the constant fighting and adventures.
It's hard to say for sure. There might be hidden twists or potential for continuation. Maybe it's just the end of a particular arc and not his entire story.
Gohan's powers are on a completely different level compared to most ninjas. His super strength alone could overpower many ninjas in physical combat. His energy blasts are far more destructive than normal ninjutsu. For example, his Masenko could probably destroy a large area that a regular fire - style jutsu could only scorch a small part of.
Rage comics can be copyrighted. If the creator of a specific rage comic has taken steps to register it for copyright protection, then it is copyrighted.