Before you start insulating the door, ensure that you take the measurements and note them down so that you can make sure that the door is a perfect fit. You also have to ensure that you have the right materials for the process. It is important that you have the insulation done by a professional so as to handle every area of the insulation process including the condensation concerns.
I would drill three or four holes in the top of door check with a light to see if the door is hollow all the way then I would spray expanding foam (rightstuff ) down the holes from the top till its full
Most commercial doors have a thermal brake built in to them. Insulating it would be difficult to do because of structural ribs in the aluminum frame of the door panel. Expanding spray foam is not a good idea.