Hello and welcome
Firstly I think this would be better suited in the growing area - no biggie, a mod will probably move it.
Secondly they do benefit, if you check shane's (stc03498203498203948023948 - ok thats not it exactly, but I can't remember the numbers after the STC part of shanes username) glog, you'll see he experimented with this for some time. The result was that YES they do indeed benefit from a dark period. The little plants are like solar collectors by day, but they seem to do their growing while "resting" at night - so there is indeed a use for a night cycle.
seems to me 12-16 hours of light was the sweet spot...
Fans are a fantastic idea and help to prevent damping off, as well as creating stouter stems which will help down the line.
not sure on the dry ice
never thought about it really... But it sounds like you are asking the right kinds of questions...
From my own experience its SO EASY to over love the little sprouts until they die. Its more of a struggle to neglect them just the right amount.
**later** I went and got the link to shane's GLOG, not sure exactly which page the lighting discussion happens on, but the whole thing is worth reading any way
especially the parts about learning to deal with a virus, and being carefull of your seed sources... Sometimes (as in shanes case) you can't help it, and you get an infection any way... but I digress.
