Tadashi himself, without his memories, would be confused. He'd see all these people who seem to know him well but he doesn't recognize them. He might feel a bit scared and out of place. As he starts to interact with the others more, he'd slowly form new relationships with them while they're trying to bring back the old ones. There could be some really interesting character dynamics as everyone adjusts to this new situation.
Characters could have mixed reactions. If the fanfic is well - written and respectful of the source material, they might be quite positive. But if it's poorly written or changes their characters too much, they could be disappointed or even angry. For example, if a character is known for being brave in the movie but is made cowardly in the fanfic, that character would likely be unhappy about it. And this reaction could vary from character to character depending on their personalities and how much they value their established identities.
Hiro would be determined to save the kidnapped member. He'd immediately start analyzing the situation, using his intelligence to figure out where they might be held. Baymax would be concerned for the safety of the kidnapped character and would follow Hiro's lead. GoGo would be angry and ready to take action, using her speed to quickly track down any leads. Wasabi would be a bit more cautious but still committed to the rescue. Fred would probably be coming up with wild but potentially useful ideas on how to save their friend.
The protagonist of Big Hero 6 was Hiro Hamada. He was a 14-year-old robot genius from San Francisco. Hiroshi Hamada experienced many setbacks and growth in the movie, eventually becoming the captain of Super 6. He was brave, kind, compassionate, tolerant and gentle. Hamada Hiroshi was a genius who loved to invent and create. He invented micro-robots and made high-tech equipment. His companion was Da Bai, a chubby, inflatable, and charged robot. Hiroshi Hamada and Da Bai formed a superpower team to fight against criminal conspiracies together. Hamada's story showed the importance of friendship, family, and courage, as well as his desire for adventure and justice.
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.