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.
It reimagines it by changing the genders of the main characters. So instead of a female mermaid longing for a human prince, it could be a male mermaid. This simple change can have a huge impact on the story's plot and relationships.
It changes the relationships. For example, if Luke was female, her relationship with Vader would have a different undertone. It could be more of a father - daughter dynamic, which might make Vader's redemption more about paternal love. Also, if Han was female, the flirting dynamic with Leia would be reversed, adding new comedic and romantic elements.
In a genderbend story, the main character is a merman instead of a mermaid. This changes the dynamic of the relationship with the human character. For example, in the original, it was a mermaid falling for a human prince, but in the genderbend, it's a merman falling for a human princess or prince. Also, the challenges faced might be different as male and female characters often have different societal expectations, even in a fictional underwater and human world setting.