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.
Demon Slayer left off in the manga Hashira at a cliffhanger moment. The heroes were at a crossroads, and the fate of the world hung in the balance. It was a point that left readers eager for more.
One of the great fanfictions could be those that focus on the backstories of the Hashira. For example, a fanfic that delves deep into the past of Giyu Tomioka, exploring how he became the Water Hashira. It might show his early training days, his struggles with his own abilities, and how he overcame personal tragedies. Another interesting type could be crossovers within the Demon Slayer universe, like Hashira interacting with characters from different time periods in the story in unexpected ways.