Im gonna recommend at your level making goblin rocket fuel and superior healing potions.
You can make some money selling them on the AH - especially goblin rocket fuel.
If you keep your eyes open for the volatile rum on the AH you can get it really cheap sometimes. You cant farm it as of yet its in a level 43-45 level area in tanaris, but chances are if you check the AH in tanaris as well as your home cities you could easily buy the rum for 1g a stack and make a stack of potions for around 3g. Sell them for around 8-9g.
To get the spell for it, ask any engineer they can make you one.
As far as leveling your herbalism your at a low level to go up high at this point. Just work on raising your level to around 30 then you will be able to go to shimmering flats near tanaris. Or other areas.
I hope that helped?