Finished my first stage of this build today and it turned out well. If I had owned the correct tools it probably would have taken only a few hours, but since I was improvising with what I had, it took a while. Some tips if you choose to go with the flat door:
When you cut around the edge of the frame, try to leave a little lip all the way around. It makes the marker board look better once its sealed.
Once you've cut all the way around the door, don't try to just pull off the panel. I found that prying the plastic away from the foam and breaking it off in pieces was easiest. Then you can shave down the foam from there. I found a flex blade to be the best for this:
Getting the outside frame out of the door took some patience with an exacto knife, slowly pulling the foam off the inside plastic. Once you have gone all the way around separating foam, you can use a flat head screwdriver and carefully pry the plastic from the outer side:
Overall I learned a whole lot doing my first project like this, and enjoyed the heck out of it. My kegging gear should be here tomorrow. I can't wait to get it all inside my new kegerator! I have a few more pics if you have any other questions.