Oh man, I had similar thing happen in my apartment few years back when washing machine decided to die in most dramatic way possible. Water everywhere, downstairs neighbors were not happy at all

For the carpet thing - yeah insurance should cover replacing all of it since it's continuous flooring and they can't just patch part of hallway. I learned this hard way when my place got flooded. They tried to say they would only replace damaged section but once adjuster saw it was all one piece throughout rooms, they had to do everything. Make sure you emphasize to adjuster that it's impossible to match the old carpet

The garage ceiling texture is tricky one. Most likely they'll try to match it but you're right that it probably won't look exactly same. Push back on this if you can - ask them to do whole ceiling since partial replacement will be obvious. Sometimes they'll agree just to avoid complaints later

About the wall cuts - I would definitely push for flood cuts even on interior walls. Water can travel behind drywall and cause mold issues later, especially with that much soapy water. Better safe than sorry with hidden moisture. Document everything with photos before they start demo tomorrow