Just a reminder - that GTX480 probably isn't going to generate any significant hashing power compared to the 5830's.
I've got 9 5830's up and running under Ubuntu 11.04 using this guide
as a basis. I setup a basic script to start the poclbm worker for each of my graphics cards (not in crossfire) and then started each one as a service. Another script runs in the background on each machine to monitor temperatures and adjust fanspeeds accordingly.
People generally say use whichever OS you're most comfortable with, but I've found that if you've got any experience with Linux, it's probably one of the best for a dedicated mining rig. Just as a disclaimer, I'm an all-Windows man at home, running a Server 2008R2 domain for my four Windows 7 computers (and yet I still recommend Linux for dedicated mining).
I was having some issues with phoenix a while back, and it seems that whatever performance benefit it had over poclbm has gone away now with the recent incorporation of the phatk kernel into poclbm.
Hope this helps.