the flange along the edge is a great idea but remember to check and make sure the skin is flat and does not have a slight curve where you are patching, you could wind up with a lot of evercoat to fix that.

 

A piece of 1/8" hardboard and a school compass works too, a little fussier to make the template, but a whole lot cheaper! The finger gauges are actually very accurate, nice and easy to use, but I would still transfer the contour to a piece of hardboard for safety sake. Nothing would be worse than just before you start to work the panel back to shape a friend (or SO or kid) comes in a says "What's this?" and moves it, or it slips out of your hand and hits the floor knocking out the contour.

 

Instead of spot welding the flange and having to grind off the welds, just place some panel bonding adhesive on both sides of the flange of the door. (between skin and outside of door and between inside of door and the flange that you hammer flat.) This is what the body shops do nowdays. You could also use panel bonding adhesive in place of the but weld and just use a backing piece (cut from left over repair panel to maintain contour) and hold it in place with a few pop rivets until the adhesive dries, then just drill out rivets and weld holes shut or fill with body filler. This should prevent the distortion caused by a long weld seam.