Hehe, guess it wasn't a joke after all. Seem to have touched a nerve.
As it happens, the only 'not sure' in my post was the amount or # of fermenters that would be best, as that OBVIOUSLY depends on an individuals needs for space and #/size of plants. You seemed to have imagined more than...
Obviously, any exhalation would still be mostly nitrogen gas, close to what you breathe in (78% in atmosphere).
I HOPE you're just suggesting the ballon thing as a joke, either that or you should abstain a bit before posting. ;)
A simple one gallon fermenting container will provide a slow...