I'd like some advice about using polymer clay both for modeling and for casting.

I have read that polymer clay needs to be baked after sculpting/modeling. Does it shrink during this process? How fine and detailed can it get?

Can polymer clay be formed around an object, baked, and used as the mold for pouring pewter?

Where does a person get polymer clay? Anything special to look for or ask for?

And somewhat related...has anyone used casting wax to sculpt a shape prior to casting? How does the casting wax compare to polymer clay for sculpting and picking up detail?