With both our kids, we pretty much fed on demand. BUT it seemed like every 3-4 hours was the norm, and I might not remember the amount real well, but it seemed like somewhere between 2-4 ounces.
Keep in mind that about 6-8 weeks, they go through a growth spurt. With both our girls, once that growth spurt kicked in, we couldn't keep them fed because they were going through it so fast!
I remember with our oldest, once she hit 6 weeks, one day she was just screaming. I fed her, changed her clothes, changed her diaper, and she just kept screaming. I called the doctor's office in tears, and they said, "How old is she? 6-7 weeks? Feed her." I argued for a bit because I had JUST fed her, but finally did while the nurse was on the phone, and my daughter finally realized what was going on and drained the bottle. I couldn't believe it - she said, "Growth spurt!" and giggled.
For what it's worth....and good luck!