Honestly, I'd say for multiboxing the same thing I say to friends starting WoW....for the first one, level it youself without and powerleveling as you will learn a lot. After that first time, feel free to power as much as you want.

If you use your lock to boost then you'll get everyone at various levels and just have to come back and them boost 1 or more to catch up to the others anyway so you won't really save yourself that much time and you won't get time learning how to get the team to work together at an early level where mistakes cost a lot less