The CPU only has a Heatsink, there should be baffles from the fans which blow air onto these (or maybe thats the G5, I haven't checked recently).
It will boot without a heatsink but it won't last long, lol
Chassis fan not needed to boot, but see previous sentence.
RAM I believe is DDR2 ECC or Buffered.
IBM RAID controllers _should_ work fine..... test and find out...