Not only will a properly sealed vapor barrier help with drafts, but it stops condensation if you use metal for the interior of your building. When the warm air from inside your building meets the cold air inside your walls, if you have metal it will condensate. This will make your ceiling drip and also ruin your insulation. I chose to go with metal because it looks nice and it is also much lighter than drywall, plywood, or OSB. For your ceiling I would definitely use metal for those reasons. Wood is cheaper, but don't forget to factor in all the time with primer and paint if you want it to look nice. Even if you have insulated garage doors they are probably only going to be like R7 at best so they are always going to be a place for major heat loss. Obviously make sure that you have weather stripping all the way around. I was going to put thicker weather stripping on the bottom of my doors, but when I had my openers installed they actually have a decent amount of downward force when closed and the weather strip that's on there now seems to be okay.