You definitely will need a tank. I took my mage/mage/priest tri group to RC at level 21 and got my ass handed to me simply because I didn't have a tank. You could run a pally/mage/mage group or a shaman/mage/mage group just so you have someone that wears some kind of armor other than rags, and you have a bit of healing to boot. As another person said, good luck with your decision and keep us posted.