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.
The '2 moons novel' could potentially be a science - fiction or fantasy novel. If it's science - fiction, perhaps it's set on a planet with two moons and the story revolves around how this unique astronomical feature affects the planet's ecology, civilization, or the characters' lives. In a fantasy context, the two moons might have magical properties that the characters interact with or are influenced by.