Via info gleaned from this thread, and some personal experience, being from the North....
If you can get 110V to the car with a long extension cord, that would be helpful. A trouble light is good, and since they have 110V taps on them, a dip-stick heater would be a good idea too. If you can’t get the 110V, I like the idea of the burning charcoal. Don’t let it get too hot! You don’t want to crack the oil pan (or more likely the plug gasket).
Either way, blocking the front end with sheets of corrugated cardboard is a must, because if there’s wind, there will be a tendency for the powdered snow to blow up into your engine compartment, which will cause complications with your electrical system. You don’t say how old you car is, you may consider changing spark-plug wires now because extreme cold kills them.
Let the car idle a good half-hour before you drive it. (This one’s a bit of a “duh.”)
Another item I haven’t seen mentioned yet: Using a Hygrometer, verify the concentration of your anti-freeze. Drain water and add AF if you must. Blown freeze-plugs will screw up all your careful plans. If you don’t have cloth seat covers, thrown some towels over the leather or vinyl to help keep them from cracking. Sit on them as little as possible until the car warms up.
(I fixed all this years ago by moving to AZ....lol)
Changing the plug wires on a diesel is difficult - best ask your dealer to do that...