They were pretty good with ours, we had a few bits missing and they turned up the following week. That was three or four years ago now though
Re the door – presume you can’t use the supplied door as the handle/hinges is on the wrong side? It is a pretty straightforward job to drill out the door and swap over. If you are painting the door anyway you can easily fill the old holes with dowel / blank and filler and it would virtually be invisible. Yes, not what you should be doing, but if the alternative is to have a shed with no door for months I’d give it a go.
Or, if its a double door, just completely removed the furniture and screw it to the frame until the replacement arrives. So you will have one working door. Again not ideal but solves the problem