This may seem like a stupid question but I've never installed brake components before. How many sets of pads and rotors would I need to buy - 4 rotors and 2 sets of pads or 4 rotors and 4 sets of pads? Last time, I had this done at the dealer. They turned the rotors and installed new pads. This time, I want to save money and do it myself. Any advice would be most appreciated.