So i always leveled as a undead and i will do the same here.
i always finish the quest line in the UD starting place til i hit around 10-12 then i ran to barrens. But i cant remmeber where u got the prequest for Barrens. I remember it mabe behing in the second town (not the troll one the one u have to run pass to get to ogrimmar)
So if anyone of u know the NPC name and at what level you can take that quest that tells u to run to the bridge at barrens i would love you forever