well looks like i got here too late..
Your goal is to get a door unlocked, and then turn the car on. After that, you leave the car alone for many minutes, while it warms up.
(hot water will freeze within seconds when poured onto a large frozen object outdoors in subzero weather. It might give you access to the door lock.)
Where to pick at the ice? Depends on thousands of factors. Which door to work on is a good starting question. One side always gets less precipitation than the other.
How to pick or break ice off a car door is hard to describe since so much depends on the ice's consistency. I have kicked door sides, and successfully broken ice, using the flex in a door panel as my ally. Once you get down to bare metal anywhere, it is quite easy to slide anythin flat and plasticky under the ice and lever the rest off to get to the door lock and handle. You don't need to remove any more ice than what is on the handle; you just pull on that handle and the door will nudge open an inch or so and that will crack the ice around the perimeter of the door. You break that cracked ice up and VOILA the door swings open -- lots of laughs when you do it the first time and it feels like it weighs twice its normal weight.
Once the motor has been running for a while its heat will loosen up the ice, and you can slide off large pieces after cracking the ice shell with a few jabs with a plastic tool (or kicks).
hope this helps.