Very nice work Greg. We think along the same lines. I am impressed you had the patience to take pictures along the way.
I did something similar but with multiple, hanging, large panels throughout a multi-purpose room. I used 1" MDF (yes, messy) and a 1/4" piece of luan plywood on the back to give it the needed rigidity, triangulation and good staple material (I stapled the fabric on). Then I cut large holes in the 1/4" luan for a little airgap behind. I also added a little frame in the middle to put a nail into to hang pictures on it...strictly for the WAF...obviously not for performance.
Also, I use acousticotton (expensive) so if my kids use a panel as a "birm," banking off one as they round the couch, it doesn't damage the panel by compressing the dampening material. Nevertheless, my finish fabric (at $16/yrd) is more than half the price of my panel (discounting the time it took to make them).
As Greg knows, take your time, plan your project, and make sure you have the right tools. It is not hard to do...but man...it takes a TON of time and patience! If at all possible, practice on a single smaller panel before making a big materials commitment. That way you will know what you are really getting into, and if you are even capable of creating a finished product that meets your quality control requirement.
I wrote up something a while back for another AVS member that described my process, but my HD crashed last summer and I am not certain I still have it. If anyone is interested in it, pm me your email and I will see if I can find it. It is a big file since it has images.