I know the best thing I did was mount 2 reels for air and 3 for electric.
I also thought the electric through a bit and made sure there were outlets where I would need them, such as by the hood of the cars so I could plug in a battery charger easily.
Since you havent decided where to locate the compressor, let me suggest this. DO one of 2 things, either mount it outside or in its own VERY well insulated room. Reason? Noise. They are LOUD.
Also - unless your running a full shop with several guys working - you only need a compressor like this one:
http://www.harborfreight.com/25-hp-21-gallon-volt-psi-cast-iron-vertical-air-compressor-67847.html