Hello urbanoid
I can see it is a while since you posted your question so I will try to answer the best I can.
I believe that by "price feed" Chitty refers to how the current price is defined. A feed from other exchanges of the current price of Silver form the basis of the current price for BitSILVER. A 200% collateral probably means that they have 200% of the invested funds set aside to cover losses. It is a way to guarantee that your money is safe with them.
Hope it helps (and correct me if I am wrong)
@ronni