If you have never boxing 5 chars in an instance, it might be helpfull to be at a comfortable level when you're starting it. So start with ramparts at 61 or so. Blood Furnace at 62, Slave pens and Underbog at 63 or so and it should be OK. Aslong as your gear isn't utter crap.

Wowhead is the best (outgame) addon there is. The more you get to know the site, the better it gets.