I ran a configuration similar to this a few years ago. I had a hard time getting 4 of them to run on a single box. It was very unstable. So I limited the rig to 3 cards, and moved the other card to another box and bought two more cards. Both rigs ran caseless because the heat was so intense. Had a large fan blowing on them running in the basement. Normally the temp down there was around 60F. The mining operation pushed the temp up close to 90F. When I would open the door to the basement, the heat would waft up. It sucked having to go down stairs to restart a frozen machine. Good thing I had ssh setup and could otherwise manage them remotely.
Power supply... for 3x5850, I used this: http://www.newegg.com/Product/Product.aspx?Item=N82E16817153106