120mm fans 8 of them

[Laser Ben]

Few as possible. Otherwise all you have is turbulence instead of airflow. And fans make heat too, specially 8 of them. Planning airflow from the start of a design is the answer.

Most fans make so little heat that it makes no difference at all.

[FourDee]

For the temp controlled fan, see post 24 and further in this thread :
http://photonlexicon.com/forums/showthread.php?t=5717

[The_Doctor]

Most fans make so little heat that it makes no difference at all.

True but I like to throw every last ounce of weight into a good argument. Actually, they tend to cool themselves, but many of them do put out heat, just looking at their consumed amps and volts tell the tale. I just don't like lots of them, on principle, because it's too easy to find reasons why one big one is better.