No such thing as too much. The baby usually will stop drinking either because she falls asleep or because the breast is empty.
I don't think there's a set standard on how much a newborn will drink, she'll drink til she's full, my doctor told me just let my son nurse until he stopped, at that stage they'll stop or go to sleep when they're all done. Just pump and freeze whenever you feel like it, then you have backups just incase!
BUMP
So how long should I let baby feed on breast before removing her... is there a such thing as too much ?
I do actually plan on breastfeeding as much as possible but when I leave for class (senior in college) and work my grandmother will be watching her for the time I'm gone and was going to pump some milk for her to feed baby.
Pump all you can get, and freeze the extra that the baby doesn't drink. It's wonderful and handy to have the frozen milk on hand. There are little plastic sacks that will screw right onto the pump. You should empty the breast on each pump session, so as to get the rich "hind milk" out of the breast.
Is there some reason you are pumping? Or are you pumping along with the breastfeeding the baby is doing? I ask because I never got even three ounces out of a breast when pumping, despite the fact that my son seemed to get more out of me at a given feeding.