1. A 80 mm fan should work fine. I usually leave about 1/2" to 3/4" clearance between drives. This works fine with the 4 SCSI drives in my case.
2. My 350W SPI power supply powers 4 SCSI (1 - 15K and 3 - 10K drives), 2 IDE drives, a DVD burner, an overclocked Barton, etc. with no issues.
3...