I use axial fans exclusively...most CFM for your buck, low low electrical usage, and they seem to last forever. 5 years on the same fans, no failures at all. You DO have to clean them every once in a while. A dirty fan blade only moves HALF the air it's rated!!! ( Even more true on squirrel cage type blowers) Fans are always on...lights? It don't matter to them plants one bit if you run them 24/7 but you're electric bill will be lower with 18/6. Regardless of light schedule always run your fans, and vent or heat as needed to maintain 78 degrees...Humidity is a far far secondary concern and not critical. They will grow at 60F, but very slowly. Read sticky's!