What Mike B said about the air drops is a good idea, but you can also just put his suggested drip leg and drain valve on just the last drop and install the ones closer to the compressor on an "arm-over" (tee pointing up and a couple of ells to the drop) and no drip leg. But to do that, be sure that the main slopes toward the end of the run. You also need a drip leg and drain valve near the compressor on the riser to the overhead mains.
As far as electrical outlets, they're like tools in that you can never have too many of them.
