Christmas Wall Hanging

I've been busy and my computer arm aches! Our church has commissioned our small group of quilters to do a huge wall hanging that will be displayed during the Christmas season. We found an old design, altered it to suit our size and space, and I've been drafting the pieces and printing them. This hanging will have three panels, 22" and 38" and 19" wide, and will be 78" long. It will have a stained glass look. We are hoping to use batiks. 

In this picture, some of the colors didn't get 'added' so where you see black, think greens, dark blue, etc. and the "leading" will not be white as it shows here.

Anyway, the plan is to make the sandwiched panels using a light-weight batting. Then we will pin all the paper patterns on each panel where they go. The patterns are all number coded and there is a printed "key" in case we get confused. Make that "when we get confused."

Then we will cut out the fabrics, one area at a time, and replace the paper patterns with fabric pieces.  We are going to sew them on through all layers, so attach them and quilt it in the same step. We also plan to put sleeves on top and bottom, to put a weight in the bottom to help it hang well and not flap about.

My question: has anyone done anything this large? If so, what are the challenges that we should be aware of? We love the look of it so far, and keep telling ourselves it will be like putting a jigsaw puzzle together.