Thanks for the thoughts everyone!
If I attach the curtain tracks -
http://www.walmart.com/catalog/product.do?product_id=5150988 at the outer sides of the ceiling, then the measurement drops to only 102"...6" more than a 96" curtain. The track & clips (or optional hooks) will take a couple of inches so I'm now getting close to working this out. IF I decide not to go the bulk fabric/sewing machine route..... Maybe a border hot glued/velcroed around the bottom, or an extra reinforced top carrier panel can get the lengths correct.
Basically I am now looking at side curtains about 102" high and 20' long each. The windows/door won't be a factor as the curtains will pull flush to the walls - any light leaks in between the panels and I could use velcro to help seal them off if need be - but again, we won't hardly ever use this in daylight hours anyway.
A couple other panels, valances and tracks for the screen and I think I'm off and running - Yes, velvet/velour might be a pain to dust/clean, but I don't think there is anything nicer looking or easier for the money! I'm going to let this simmer for a couple of days and work it out on paper before buying the materials, but so far this seems like the simplest, easy to install, lowest cost option.
The screenwall pic below is from Ronnie over on avsforum (
http://www.avsforum.com/avs-vb/showthread.php?t=638024 ) but matches my room plan almost exactly. I won't build the upper soffit, and the stage may only have one step...and just side curtains, no fancy side walls as he ended up doing - but it still looks pretty cool!!