Being new to the horde, I suggest a run to UC and take the translocator to the BE starting zone and then eventually to Ghostlands. The quests in those areas are very multibox friendly. I leveled there exclusively with my paly, priest, 3xmage BE team and I finally left ghostlands level 18, 5g on each character, and good enough gear to one shot all of SFK. I tried to do the same with my 5xshaman tauren team and found it to be MUCH slower. The barrens is just too wide open.