Answers: I am a alliance player but in this situation is is the same for both sides. I be able to be exalted with adjectives 5 major alliance factions by smooth 40. At the time that was when you got your mount but I be able to have any party mount I wanted by then. The earliest you can be is somewhere around within since unlike factions like the timbermaw, nearby aren't mobs you can grind for rep. The quests to get rep lattice exp so I would say somewhere mid thirties is the lowest possible. If you want rep as fast as possible you simply have to do every races quest and after you get out of the level 10 areas you catch splash rep. Say you get 100 rep with Org later you will get 25 rep with the other largest factions. This paired with cloth turn ins is the best opening to go.
You Can Be Exalted From level 1, but you hold to complete quests to get rep, so you probably won't be lvl 1