Good luck with going back to work. I just went back and this is what I discovered.
I agree with the pp about the Medela Pump in Style and the storage methods. Before I went back, I had 30 oz of frozen milk stored. But, now that I'm at work, I can only pump what I need for the next day. We're each different though and you may be able to pump more.
Good luck with everything. I would advise that you start pumping a couple weeks/months out or more before going back to work to get a supply up and see how it works for you. With my first, I couldn't pump, but then again, I could hardly bf effectively. Education and support work wonders for making through the difficult and/or confusing times.