Scott, I've done it all ways. If you have to lift the body with people...The more the better. 4 people can lift a car with fenders, glass, and headliner. As proof by Alan's 56 ragtop we did 10 years ago. Doors can add a lot of weight, but are crucial to bolting the body to the pan. You can distort the shape of the door opening by shimming the rubber pads on the beam and rear shock towers. I like to at least have the door bolted/adjusted to the body so that I can watch door gaps as its tightened to the pan.http://www.kustomcoachwerks.com/forums/viewtopic.php?f=13&t=2024&start=436
The main reason I like to build the entire shell and pan before combining them is for the ease of assembly. I'm not as young as I used to be. The less bending, twisting, and working on my knees, the better I am. The lifts are a game changer in this department. They make my job easier and faster.
Also, if you look at vintage VW factory pictures, you'll see that is how they did it too. I find myself trying to replicate VW procedures.