A:Answer16 gauge. I used 14 for the back left speaker since its the farthest and longest to hook up. The rest I kept on the 16 gauge. Make sure to buy some extra wire just in case like another 25-50 ft depending on room size. I would have ran out using all the 16 gauge if I needed it for the back left (sl) speaker.
A:AnswerYes. It comes with about 50 ft. of wire which is JUST enough for a medium sized living room. I would recommend picking up an extra 50 - 100 feet just to have on hand. Depending on the size of your room you may need it.
A:AnswerIf you look at the rear photo of the receiver you will see speaker connections for the two surround (rear) speakers. It leads me to believe that all speakers has to be wired to the receiver.