I just started leveling here, and from my experience, at least as draenei (never played alliance before), there's plenty of quests and i feel like i've never leveled so fast before. So i think it shouldn't be too big of a problem to level 2 chars.
just level in tbc areas (if ally azuremyst and bloodmist) they give nice dropss and got plenty of quests focused in one place so you wont have to wander the world to find one.
concernign party leveling: the exp rind you get from killing mobs is shared but not the quest reward. If you plan to level making quests a party is sa very good option allowing you zero downtime and easily doing elite quests. dont think to be crippled for having 50%exp share from mob grind you will complete quests a lot faster means more exp per hour