I pump EVERY time it's time for him to eat (after bottle feeding him), and I currently produce 4-5 oz of milk at each pump. I didn't think it was a lot, but my LC said it was a good bit considering the average of what a mom of 3 weeks would get when she pumps. (She jokingly reassures me that since I'm pumping gallons he won't be going hungry etc
So now that he is starting to hang out on the breast again and actually move milk, I still pump somewhere in the neighborhood of 2.5-3 oz.
Pumping for 3 weeks has not at all hurt my supply--and breastfeeding wasn't even well established yet for me.
(What did hurt it, though, was those non caffeinated sodas that I thought I could get away with. Just drink water. :O )
I haven't returned to work yet, but I will in a few weeks. I'll have to pump while at work and BF while at home (like you..).