As of the current manga chapters, Sanemi is still alive. His character has gone through many challenges but has managed to survive. The plot continues to unfold with him as an important part.
Since I don't have specific details about this 'sanemi light novel', it's hard to say precisely. However, in many light novels, the plot often includes elements such as a unique setting, be it a fantasy world or a post - apocalyptic one. Sanemi might be at the center of a mystery or a power struggle. There could be a love interest involved too, which could add an extra layer of complexity to the story.
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.