1. You can't. It's possible to replay the scene if it was unlocked during christmas, but it's not possible to unlock it anymore until next christmas. ;)
2. You can't. No further floors exist at the moment.
3. Switch left or right in the quest log to see active, finished or all quests.
I can't say yet. :/
But you can follow the game to stay up to date and get a notification when a new update is released. ;)
It's also an option to join us on discord at https://discord.gg/A79WrBq
No, it won't help you to change your date on the system, as it's simply disabled in the current versions. :D
Maybe someone who has the christmas special unlocked can give you his save file. There aren't many people actively talking about the game here on gamejolt but I would bet someone on our discord channel can help you with this. ;)
Discord: https://discord.gg/A79WrBq