Zoro could react in a rather gruff way. He might say something like 'Nami, are you out of your mind?' But deep down, he might be secretly flattered. After all, Nami is an important person in his life. He'll probably need some time to process this unexpected turn of events and think about what it means for their relationship, both as nakama and potentially something more.
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.
Luffy would be over the moon. He loves new adventures and a new baby on the ship would be like a new kind of adventure for him. He'd probably want to play with the baby all the time. Sanji would be a bit jealous at first because he has a crush on Nami, but then he'd also be really happy for them and cook all kinds of delicious food for the new mother and baby. Usopp would be making up all kinds of tall tales about the baby's future, like how the baby will be the greatest pirate ever.