Re skuggoman, I would have to say not go with boomkin as a tank. They are great in the mid levels (post boomkin and pre 60) and average afterwards but the issue is as mitigiation becomes a problem, gearing your boomkin to act like a tank will make for a crappy boomkin because there isnt gear that has high def, sta and def rating as well as int and spell dmg/crit etc so you would have to choose. Now if you plan to go feral later to tank the bigger stuff thats fine but dont expect mister boomkin to be working as a tank much further than hellfire...
If you want a tank then roll a paladin, easily the best choice for multiboxing tanks hands down. Follow this up with locks/spriests (1 priest 3 locks would do fine)