At 5.5 months my son was eating cereal in the mornings and (if I remember correctly) two other meals a day. We have a big eater and I know at 6 months he was eating three meals a day. Cereal and about 6 ounces food for lunch and the same for dinner. Honestly though, your baby will let you know how much he wants. A baby that young is not going to overeat. They eat when they are hungry and stop when full. Just make sure he's getting the right amount of formula/breast milk and then feed him 'til he turns his head or becomes disinterested.
