You can never have enough fans to move the air though the case. Like was said above if you do not remove the warm/hot air away from the devices then this will cause dammage.
I have two towers in my Amiga system one for the A4000 and the other for my SCSI drives and TBC's. I have 4 fans in the A4000 tower and the other has 6 and both after running for an hour both are removing noticably warm air.
