11.That's not a solution just want to confirm your ghost stuck there too. If yes, then it should be resolved in next update.
9.I'm not seeing any problem with Mei. She appears as she suppose to be. Only time she doesn't when you ring the bell or decided not to take off her blindfold(check your "meiHouseChars" this value and see if third digit from right to left has 4. If it does her questline is failed.).
12.This one I'm sure they work because I had a shy when I was checking Izumi's bug on an exported project. If you playing on bigger maps, depending on rooms it's difficult to find UVs.
The shadow for the time being. If I confirm that Ryoko dies then you have to deal with that character.
That's not an official questline. Just wanted to show how complex you can make one for yourself. It will not stay in the game for too long. It will be removed 0.5.