Building a hanging folding door partition
" bottem pivot would need to be able to withstand a lot of side pressure when the doors were not deployed." Most of stress is going to be at top, folded or open. Bi-fold hinges are designed for that stress, and are available for regular interior doors, probably not at big box store though. For easier installation I'd look for non mortise hinges. Installed in standard way, no more stress on unsupported pivot of several joined bifolds than one door.
For heavier door, there needs to be a hanger at every other top pivot with angle support to corresponding pivot. I'd certainly use aluminum for any metal braces. And i would not rely on any style hinges for any support. Even though there is no bottom track, rollers, especially under non hung pivots, should be used. I've never purchased doors for any that I have built. They were usually a bit more decorative and were basically 3/4 to 1 1/2" thick, two sided raised panel cabinet doors. Sometimes had to route groove or sandwich in aluminum channel to resist warping and twist.
Robo, regardless of what panels you use, hanging and support hardware is where most of your attention should be. I don't know height of your ceiling, but assuming 96", you can cut inch off top and bottom of standard 80" door or bi-fold. I wouldn't go any thinner than 1 3/8, without bottom support you will get warpage and twisting. Standard 36" bi-fold will run you about $35-40, will come with most hardware you need, fold into two "packages" a bit over 18"X 8 1/4". Standard 36' hollow core will run $20, will have no track and roller, or other hardware ( regular 3" hinge will work, with extra support, but I'd go longer) will make package 36"X 4 1/4. Weight of each 3' is about 30 lbs., 180 lbs + hardware, so be sure track is strong enough.
I think one 18' wall will be a bit unwieldy, especially to close, it will make folded pack same width but twice as thick. Either way, you'll need some sort of hook and eye, or cam latches that will pull wall straight and firm when closed.
I kinda think robo has given up on idea, and we are now engineering and desiging this on our own. Anybody got any color preference? I'm leaning toward distressed, aged, raised panel, rift cut oak and antiqued, vertigred brass hardware.
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.