When I was building up a supply of EBM I would express just once a day, during the morning feed. By this I mean I would have a baby on one breast, and a pump on the other, to harness my baby's ability to stimulate let down. It is handy to have some EBM in the freezer, but you probably will not need it until bub is a bit older so if I were you I would concentrate on bub just now, and worry about expressing in a few weeks once you have breastfeeding mastered.