We started using formula once a day at 6 weeks, she was gassy and had bad stomach pains on regular formula so we switched to soy, still a bit gassy, but went away over time. Not sure on the amounts, right now we do 7 oz over three feedsin the day and a small feed at bed time (3 or 4 oz), but at one point she could pound back 9 oz in a sitting.
HTH
Heidi