E.H.
I am not sure it is a habit. At 6 months that is a long time to go w/o food. All the babies I have known, including my own, still wake up at LEAST once a night at that age. He is waking up because of hunger, or something his body if feeling. Those are the things that their bodies respond to, not wanting to develope a habit.
I am also not sure if 5oz is enough? I have a feeding chart given to me by my second babies Dr. It says usually at this age they are up to 6-8oz 4-6 times a day, and 2 servings of cereal.
Good Luck, it is hard being a first time mom. I wish I had known about this site when I was. Eventually you will forget about all the sleep deprivation and will wish you could go back to them being a baby again! :)