Your plan and vision seem creative, as well as ambitious, but I think you will curse yourself if you don't invest in more of a sign printing machine rather than an aqueous fine art printer.
Take a look at Mutoh (ValueJet-rotten name, nice printer), Mimaki, and Roland eco-solvent or mild solvent printers. You will spend more initially, but recoup it in operating expenses and SPEED. For the environment and viewing distance you are talking, a sign printer will be more than up to the task, imagewise, and more durable. With solvent printers you can get away with printing on uncoated material, and can also print directly on vinyl scrim that isn't as nice a texture as canvas, but is more economical and durable. Another advantage of a sign printer is that they are built to do roll to roll printing. That will take a big hassle out of the process in one fell swoop.
Sign shops typically use clear laminates instead of spray or roller coatings when they want maximum durability, but you can spend almost as much on a good laminator as a wide format printer. You are talking about changing graphics often anyway, so I'd take a chance, and reprint if there's a catastrophe, but try to avoid coatings or laminates altogether to save time and money with an additional process if I was doing 10' x 200'+ every time.
As for stretching, I spent 28 years in the scenery and modelmaking business, and in my previous life, we'd have hand stretched and stapled these on the back by hand. It's no small undertaking to do that much, but you will get it down to a system over time. A rolling table the size of your frames will make it more efficient. If possible, a second set of frames would make it much less rushed and painful for each turnaround.
You probably already have it sorted out, but I'd mount a type of museum cleat idea on the wall, and have the top of each stretcher frame have an inverted u-shape that hooks over the wall cleat. That way, nothing sticks out of the back of the frame to damage the next one when stacked, the cleat keeps the frame from moving left and right by being as wide as the frame, and all you need at the bottom is a keeper screw or two into a bracket on the wall. The act of hanging each panel can be made almost painless. Your biggest time spent will be in printing, removing canvas, and restretching.
Best of luck!
