The RAID should not need to be reformatted for any reason, but absolutely back up everything on that array before you make the switch, just in case. Might not be a bad idea to simply wipe that array clean and then put all the media back on it when you make the switch.
Absolutely, positively don't switch machines until you're at a comfortable place in your production schedule to deal with any unforseen issues. Better yet, if there's a way to start running your new machine while keeping your old machine active at the same time, that's the best way to make the transition. I was able to do that with our transition to the Mac Pro.