First of all, welcome to Chinclub.
As far as a mat for the floor, you can just buy fleece from a fabric store and line the bottom with it. I use kiln dried pine for my bedding, its really cheap. The cheapest place will be at a feed store. As far as a house for him/her, you can buy a little click-together pine house from Petsmart if you want it now. I do most of my business through
www.lonestarchinchilla.com/ they are awesome. For the wheel, a metal flying saucer or a chinspin seem to be the best. I have a chinspin from
www.qualitycage.com. They are pricey, but chins love them and they are basically silent. As far as rocks, they really wouldnt mess with them much. So i would think as long as they arent small enough to eat, it will be ok. As far as the branches, I would recommend using apple branches.
As far as your food, this is important.. Nutriphase isnt very good. There are a bunch of places that sell good brands, Mazuri, Nutrena ( i use Nutrena ), there are lots more. Normally, you can buy them for about a dollar per lb. Which is cheaper than your Nutriphase.
Most of all, enjoy your new friend