I think without really heavy surface colonization to start, you're maybe leaving some yield on the table, since you may not start getting great coverage until the second flush. But I'm just speculating/guessing. I ended up pulling over 4 dry zips from 3 12qt tubs, even with a weak start. I went into it expecting utter failure, so I was pretty amped about producing anything at all.
You want air to enter and exit the tubs, that's 'free air exchange'. It's necessary. If you're running a humidifier, I probably wouldn't worry until you have an actual reason to. It was maybe 40% RH when I did my grow, with no humidifier. I just misted daily. Sure someone who actually knows will chime in eventually.