1) in my experience, it depends on the snake. All but one of mine will eat in shed. My butter absolutely will not...It's just a matter of trial and error and learning your snake. With a small rat pup, you will probably have trouble keeping it alive for a week since it hasn't weaned off the mother yet. The only other options would be letting it go (it will die) or to euthanize it.
2) All of mine poop simultaneously with shed. I would definitely expect it.
3) Moss helps. You could even put a small clump in the hide with it. Otherwise, some dampened coco husk would definitely help.
I just fill the water bowls up all the way for mine when they're in shed and it provides plenty of humidity, but I use tubs.
Good luck and keep us posted.
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