I think this is one of the biggest questions that I had too! No one ever had a good answer for me, so I muddled my way through it. My daughter is 7 1/2 months old now....and thriving. Once you figure out the formula, then you add solids----and start all over!
One note that I took in a parenting class at Harris Hospital said "Feed a baby the same ounces as the age of the baby in months + 2 oz.)". I didn't find that this worked for me. My daughter spit up a lot in the beginning. Around 3 to 4 months old, she was drinking 4 oz bottles every 3 hours. Now, at 7 1/2 months old, she is drinking 5 oz. bottles every 3-4 hours. And, she takes a 7 oz bottle at bedtime along with some cereal and fruit.
I truly believe that every baby is different, and you have to take cues from your baby. I tried asking some friends of mine about how much to feed my daughter, and ending up over feeding her, and she would spit up. My friend told me to feed my daughter 7 oz at 4 months. WAY TOO MUCH!
I know it is hard, but your baby will help you! Good luck!