it will take roughly 25-28 lvls to get exalted with the guild. after roughly a week in Stage Clear, my alt is about lvl 25 and i am 40% through revered. you need to turn in green, yellow or orange difficulty quests to get guild rep. also keep in mind the gold needed to buy the pets.
Thundering Serpent Hatchling - 300 gold - requires Revered
Lil' Tarecgosa - 1500 gold - requires Exalted
you can also pickup the Horde guild page(300gold) & guild herald(500gold) if you dont already have them.
couple of things to consider
1) buy the Illustrious Guild Tabard(125 gold) at Friendly, and the Renowned Guild Tabard (250gold) at Honored for the guild rep boost. otherwise it will add another 15-20 levels to get to exalted.
2) class consideration
- a) monks are very strong at low levels and get a free daily starting at lvl 20. Thats an extra 275 guild rep with the tabard.
- b) DKs start at 55 which would allow them to travel around easily and do the Pet Battle dailies. Guild Rep + chance of stones...
3) you can take the "defeat the Pet Tamers" quests on your alt in Ogrimmar, and them complete them on your main on a different server, and them turn them back in on your alt for the guild rep.