Gotcha. I say wait until the story is complete. If that is 30K, then so be it. The key is just making sure teh story has everything it needs.
Then get started in your querying. Many people sell series/two book deals without even STARTING the second book, so you're ahread of the game.
Next, I'd say start somethign totally fresh and independant, so that while you're working at getting an agent for book 1, you have a back-up plan.