Regarding the PSU or PSU(s) the newer nVidia's e.g. getting the Quadro vibe or FirePro are more efficient and you might get by with a single large PSU.
Here's an excellent PSU sizer -> http://www.thermaltake.outervision.com/ IMO for Rendering use: 1. 100% TDP, 2. 100% System Load, and 35% Capacitor Aging next if it's on 7/24 then look at Gold or Platinum certified.
If you post: 1. CPU OC, 2. HDD(s) number, 3. GPUs, 4. other connected doodads I'll be happy to suggest a couple PSU's or Dual PSU's...