For the library, maybe add a stepladder to the corner in question? (I'm a children's librarian now, but when I used to work in a Special Collections department, I was up and down ladders all day long. It was an actual workout.)
For the kitchen, I would suggest the hallway wall (it's a warm, golden yellow) or the Pompompurin wall as my second choice, if it wouldn't feel overpowering to you. I would replace the 4 chairs with Pompompurin chairs, and replace the white minimalist table and the white dresser with natural low tables to match the other dark wood in the room.
For the bathroom, it has a really nice spa-temple feel. Maybe add some stone lanterns in the lower corners, and a deer scare for a meditative noise? I'd keep all of the items you already have in there.
In the bedroom, the pink and red flowers seem to clash, and so do the sloppy wardrobe and the taller one next to it. (I know you said you want to keep everything, which is cool of course, but that's what stands out to me.) I'd add in more of the classic series, including the round classic table as a nightstand, and a few smaller teddy bears to go along with the giant one. Maybe move the clock to the center of the back wall, and since it looks like you might be using the clock as a headboard (?), move the bed to be in front of it. A fireplace might look good in here, too.
Just some suggestions based on my initial impressions. I like your rooms a lot!
I'm a librarian so I have to chime in for the library--
Hello, fellow librarian!
