I'm currently running a team very similar to this, Pally/Mage/Mage/Rogue/Shaman. I'm having a blast going through dungeons and can't wait to hit 80 to start blasting through heroics. I currently do most fights with a 3 keys... one key for my DPS rotation on the tank + 3 dps, and two keys (one per mage) for missile barrage procs.

As for when to use the missile barrage it's absurdly easy to manage...

http://www.youtube.com/watch?v=7fGoRUmdQY0

As for buffs, I run Blessing of Sact on the pally, Wis on the mages and shaman, might on the rogue... I use kings drums, fort scrolls and mark drums...