My kids are now high school and college age - so it's been a while but I loved nursing my babies and I believed that - if possible - mother's milk is the best option. It's not always possible to pump and I get that - but if you can do it - it's a great gift to give your child. If you can't - well we live in the 21st century and formula offers a good option.
I pumped in my office a couple of times a day when my kids were infants. I learned a lot from another mom in my office whose kids were about 5 years older than mine.
1 - Always get yourslef a glass of water or some other beverage and drink it while nursing or pumping - you can't produce fluids unless you replenish. Be deliberate about that.
2 - YOu will produce as much as your child needs. Supply and demand - As baby grows and needs more you will produce it.
3 - Get a good pump - it makes a HUGE difference. I tried a cheap hand one at first and it was awful. Then I bought a small medela pump that was a huge improvement. But with my second child I bought the dual Medela pump a case and a plug. I could get the pumping done really quickly.
4 - YOu don't need to buy the expensive medela storage bags. I bought the playtex bottle inserts, some good clips and would pour the milk into the storage bags and chill them in a small upright insulated bag with one of those blue freezer blocks. My coworker/friend told me not to freeze it at work, just chill it until I got home becuase you can't thaw and refreeze breast milk - it gets sour. (it's no pasturized like store bought cow's milk). but once home I'd freeze it.
5 - I used heavy duty freezer bags to store the playtex bagged milk in from the time I pumped them and put them in the insulated bag - then into the freezer at home. EAch one was dated with a sharpie so our babysitter could use them by date.
6 - Insturct babysitters or daycare workers to thaw the milk in warm water - just put the bag in a coffee cup of warm milk. - they may have to re-place the wamr water a few times until it gets to room or body temperature.
With my first child, a girl, she only had formula one time in her first year - I was a little (more than a little) obsessive about it. Even when she began to drink milk I still nursed her at bed and nap time. My son was a different story - he was always STARVING. So I pumped as much with him as I did with his sister, but I was OK with giving him formula if he needed it. so the ladies at daycare had formula as a back up if needed. If he finished the breast milk he's then get formula.
AS you prepare to go back to work y0ou don't need to have weeks of milk in the freezer - you really only need one or two days ahead of you - but I understand the "need" to have a reserve stockpiled. I don't recall but I assume I did - it just gives you some emotional security.
What you'll find when you get back to work is that your breasts will let you know when to pump. You'll get very full and rock hard boobs and if you don't pump you'll feel like you might explode. I would pump once in the morning (10:30 ish) and once in the afternoon - around 2:00. I observed that I produced more in the morning than the afternoon - it could have been stress, it could have been the natural rythm of things. So I made a conerted effort to drink a lot of fluid in the late part of the day so I'd have a supply when I got home.
You will figure out how to do it and set up a routine that works for you. I had an office where I could close the door and have privacy. I feel for the women who don't have that kind of arrangement - unless there's a nursing room - which would be fabulous!
The strangeset place I had to pump was in the bathroom of an airplane on the way back from a client meeting. I know I annoyed another traveler becuase I was in there for at least 20minutes - but it was the late afternoon and I hadn't had a chance to pump in the morning. I was leaking through the pads and my sweater - and soon my suit jacket...! Another time I pumped while I drove - luckily it was winter and had gotten dark but I was in heavy traffic and knew it would be at least another 90 minutes before I got home and I had been at a client's office all day!
The things we do for love!