Wow. That's a lot of questions...most of which you should know BEFORE getting your new chinchilla.
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Congrats on your new little one. She sounds scared. Lots and lots of patience and consistency. What kind of wheel do you have in there? Most of the time they are not recommended until at least 6 months of age because they are growing and need all of the nutrients for that.
Giving your chin to a friend to keep in the cage with hers is absolutely NOT an option. Absolutely too risky.
Clean the cage very good before you go, have the person come daily, and clean when you get back.
What kind of bedding are you using? If it's pine, you may need to spot clean daily the place he normally pees and replace with fresh shavings. You mentioned metal shelves. Are there any wood ones that need to be cleaned and sanded or replaced?