T.M.
My lactation consultant stressed that I should pump as often as possible (not always easy) to keep up the milk supply. It's better to pump more often than let your breasts fill up. Drink lots of water to stay hydrated as well. You also can start pumping at home right after or before feeding her to store up milk and to build your milk supply. But I wouldn't worry about too much about the milk supply: once you're home again your supply will easily build back up if you're breastfeeding often. I also wouldn't worry if you can't pump enough and have to temporarily supplement with formula--I could never pump enough and I practiced extended breastfeeding with both my babies (nursed for over a year).
Good luck
T.