1 to 2 to start
works as supply & demand.
The more the baby feeds or you pump, the more you'll produce. Just remember, the baby will generally be more efficient than the pump, so he/she is probably getting more from the breast than you are able to pump (in case you're worried the baby is getting enough). Eventually, as your baby grows & feeds more, you may be able get as much as 6 oz at a time.