First of all, relax. No matter what happens, have fun with the process, it truly shows to the casting team and it makes their time easier. Remember that they want you to get the job and to be the most talented person to grace the earth, they aren't there to give you a hard time.
Dancing Through Life is not the ideal song not only because it is from a popular show at the moment, but because you will be auditioning for the show that it was from. What other musicals are you familiar with?
As for questions to ask-- the less the better in most cases. Asking when you will know by isn't a good thing to question them about because they probably have a very loose time frame, if one at all. They could call you back the very next day or within the year or even remember you a few years down the line. I hope that I helped.
Beyond talent lie all the usual words: discipline, love, luck- most of all endurance.