Some characters might laugh. If the fanfiction has humorous elements, like a comical take on their battles or relationships, they would find it entertaining. For instance, if there's a fanfiction where the Sailor Scouts accidentally swap powers and get into all sorts of wacky situations, the characters themselves might chuckle at the absurdity.
Inosuke doesn't become a Hashira in the manga. The story progresses with him having other significant experiences and achievements instead of achieving that specific position.
It's hard to give an exact number. Different story arcs and battles led to the deaths of multiple hashira. Some died heroically, while others met their fate in unexpected ways. The count changes as the manga progresses.
Definitely not. Genya remains outside the ranks of Hashira throughout the manga. This is because of a combination of factors such as his skills, experiences, and the overall direction of the story.
Her friends, the Sailor Scouts, might be initially shocked. But they would probably quickly come around to support her. They could offer practical help like helping with her superhero duties so she can rest during the pregnancy.