S.J.
The best advice I can give you is when you pump, do not feel guilty for one second about missing work. Think of it as your time. Think about your baby. Relax. Take those 20 or so minutes for you. Take even longer in the beginning as your transition time. Smokers take breaks - you can too.
Get a cooler and cold pack to store the milk all day until you get home. I got one that fits the bottles right in there nicely - medela.
Keep snacks and water at your desk at all times. You will be amazed how often you need to eat. You should be nourishing your body constantly throughout the day.
I don't use the microwave bags except for about once a month to do a steam clean. Other than that, I wash the parts out by hand once I arrive home. Do not bother washing them out at work - use them each time you pump and give them a good washing upon arriving home. Medela makes cleansing wipes you can use to give them a quick wipe down after each use.
Make sure you have a good pump. I have the medela freestyle. Works like a charm. I am able to pump more than what baby needs. I shut my office door and twice per day, it is just about me and baby, even though baby is not with me.
I was surprised that I didn't cry when I went back to work that first day, or even the second day. My tears came many weeks later when I was sitting at my desk one random Wednesday. I just missed baby so much. But, I closed my office door, cried, and moved on. Don't be afraid to call the sitter/day care, multiple times per day if you want. Cry if you want. Many moms do it. Don't put pressure on yourself to be "normal" - you are no longer allowed to be normal. You are a mom.
You can do this. We all have done it and survived. Work your butt off now so you can spend time with them later when it really *counts* - right now, we miss them WAY more than they miss us. Baby has no idea you are gone (for the most part) and is interested in eating, sleeping and pooing. Pump that milk and relax. It will all work out.