A few thoughts--
Does the unit have a starter or combination starter on it? Although the plug may qualify as a disconnect for the motor, a switch would be nice. In an emergency, I would not want to unplug it under load.
The 3 #12s don't seem to be a problem, but at 480 volts, an EGC would certainly provide a much safer installation.
Also, depending on the size of the shop, more than one receptacle would be nice. This would minimize cord length, and the likelihood of it being damaged.