In the late game, elixers are VERY useful in Kara and other instances, along with gems. But, alchemy is also one of the skills that you can actually benefit from while leveling. Jewcrafting can help late game, but while leveling, when you make a new necklace, you are just going to sell the old ones. With Alchemy, you can use the elixers you get, and share them with party members in instances. Also, with alchemy, people are going to keep coming to you you your 24 hour cool downs. And, if you proc, you can use the extras, or sell them on the AH. Also, guildmembers will be wanting the elixers, potions, etc. that you can make for Kara runs, instances, and other things. Any leftovers, you can sell on the AH for a LOT of money. JC, along with being hard or expensive to level, only benifits from the 350+ levels. And by then, you'll probably be in the Outlands, which is ways away for you. Unless you really want to go into mining and JC, I would go Herbalism and Alchemy.
If you want pure money, then go into Skinning and Mining, or Skinning/ Herbalism. You won't waste your materials leveling, and you make a lot of money selling your finds on the Auction House.
Hope this helps.