I have to ask now, do you really expect us to make that ridiculous triple jump onto the spinning block? Cause I made it, and it was kinda, really hard. I'd have to agree on the size of the cabin, too big. I have no idea why you put the two undefined FLUDD boxes, but I assume that's not intentional. Also I wasn't able to grab that red coin, too hard and I fell off the roof several times. And last thing, make some sort of water source on the higher levels, because I was kinda annoyed when I finally made it up to the red coin, only to find out that I have like 5% of water left and will have to get up there ALL OVER AGAIN if I want more water.
As for the indoors, you could put windows with platforms serving as window sills. You could also try and make a plant in a plant pot (the plant being something small like a cave plant or the cactus tree and the pot would be still rotating block with some wooden texture). You could put some shelves with water on them, and you could give some sort of animal in a cage, like a cheep cheep in an aquarium or a goomba fenced off, or something. Here's something I made in your cabin:

Speaking of the bottles, they didn't appear for me for some reason... weird.
You could put also other things like framed pictures of an item (shell, enemy, whatever). The frame could be 4 wooden/metal platforms with a tile in the middle, or maybe just a sign.
As for the difficulty of the level as a whole, nothing was too difficult except for that one jump I already mentioned and the red coin. I liked the timed challenge with the switch, since you kinda bait players at the beginning, but falling off means making that weird jump again, which was kinda annoying.
Hopefully that helped.
@EDIT: I'd have to agree on the music aspect also. It's too happy for the "backstory" and not really fitting. If I had to give a recommendation, maybe something like this:
https://www.youtube.com/watch?v=ieapBou_3cs - Snowman from Earthbound
https://www.youtube.com/watch?v=oYdgznePD5k - Freezeflame galaxy (Ice theme) from SMG
Either that or you could just change the "backstory", since it's relevance to the level starts and ends before you even start the level.