It looks like the lower hinge on the driver's door is gone, but I would still remount the door with the upper hinge and even tack it in place after you get the gaps adjusted. Then go inside (or crawl under wink ) and weld some bracing across the inside of the door opening, as far down as you have solid metal on the A and B pillars, and another up near the belt line.
Your plan with the floor is good except that you have no good reference currently for the front to back dimension. DO NOT depend on the replacement floor pan to be correct.

You should be commended for taking on that project. As the other guys have said, take it one step at a time, and DO ask for help here. We want to see the finished project. We can help you produce something you can be proud of.

You can do it. thumbs_up


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.