As for oil in the compressor - just ask the shop you are buying it from. They are the people who should know for sure.
From what I have gathered from this page, the auxillary fan kicks on when the gas in the a/c system reaches a certain temperature. There is a switch on the reciever/drier that senses the temperature. The bigger switch on the reciever/drier (the one about the diameter of a quarter), controls the compressor (turns it off if the gas pressures get too high or drops too low).