1. Maybe. You'd probably have better luck with an older one, but they're designed more for personal cooling than serious air movement, not to mention newer ones are very loud for the air moved. And you won't find any 6 inch box fans anyway.
2. There's no difference between a fan and an air circulator, those are just marketing terms. A blower generally has a blower wheel instead of a traditional fan blade and is intended for drying stuff out, that may work for your small opening but will still be loud.
3. Never heard of that before so I can't help you there sadly.

You could maybe go with a twin window fan for your small opening size. Small fans inherently don't move a whole lot of air but I think it would still work even if it takes a bit longer. If you get one that only runs one direction, those tend to move more air than the electrically reversible ones. I've also heard good things about this particular model.