As Diablo mentioned, providing them with their "dust bath" is very important for their health and well being. Click on the link Steve provided, then click on "Chinchilla Dust and Baths" so you get an idea of what you need.
With those big ears, you can bet that their hearing is very good. I would not put a radio near them or put them in a room that will have any loud music. They stress out fairly easily.
As far as growth, they get big pretty quick. They will get close to 2 pounds if I remember correctly, about like a small rabbit.
