One key element could be his origin as a human. His human experiences surely had an impact on his demon self. Another might be any significant relationships he had before becoming a demon.
Upper Moon 4's back story could involve a tragic event in his human existence. Maybe he was betrayed by someone he trusted deeply. This betrayal could have been so severe that it pushed him over the edge, and when he was turned into a demon, his new nature was shaped by that past hurt and anger. His actions as an upper - moon demon are likely influenced by the unresolved emotions from his human days.
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.
Some Avengers might be suspicious. For instance, Captain America, who values order and loyalty, might be cautious about Moon Knight's erratic behavior. Iron Man, on the other hand, could be intrigued by Moon Knight's technology, especially if it has any connection to his lunar - based powers. Thor might see him as an interesting mortal with a connection to a different kind of divinity compared to his Asgardian gods.