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.
One common theme is family loyalty. Given the strong bond within the Kamado family in the original story, this is often explored further in fanfiction. Another theme could be redemption, especially when it comes to Nezuko's situation as a demon. Writers might also focus on the theme of survival, as the family has to deal with the constant threat of demons.
Demon Kamado family fanfiction can be really exciting. It could focus on the untold stories of the Kamado family. Maybe there are stories about their ancestors and how certain family traits were passed down. Some fanfictions might also create alternate universes where the family has different powers or face different types of demons. It gives fans a chance to expand on the original story and get creative with the characters and their relationships.