Hi Toolarge,
Here's a few answers to your questions, I've gone through this twice and have gotten a lot of advice myself. I pumped on top of feeding for my second and it was a lot of work.

1. You can't pump an entire day's worth in one sitting, at least not in the beginning (minimum 24 ounces once baby is a couple of months old). The breast doesn't actually work that way, it's a supply and demand thing. Most babies feed every 1.5 to 2 hours so that is typically when you would pump. Most places have laws about accommodating breastfeeding women at work, you'd have to look into your location. Where I work, I know people who just closed their office door and pumped.
2. Theoretically you could lose extra weight by pumping more, but you get into a horribly vicious cycle because you get REALLY uncomfortable if you miss a feed/pumping session. It could also lead to plugged ducts and mastitis. Also, pumping isn't as efficient as feeding baby directly, so you would have to pump longer and sometimes more often to get enough milk. Babies also tend to drink more from a bottle than the breast, so that would also require more pumping.

Some other comments about breastfeeding:
- Pumping is a LOT more work than feeding baby directly (not in the first few weeks, but after a while). I used to pump for 30 minutes to get what my kids got in 10. Plus you have to wash, sterilize, prepare and heat bottles, an extra 10 minutes per feeding. And, if you are out and about, you have to do this where you may not have any tools. In the middle of the night, it is really easy just to bring baby in bed and feed them while you sleep (instead of getting up and preparing a bottle, feeding and then trying to get back to sleep). The first several weeks are really hard, but after that, it is so easy to feed your kid.
- some babies start to prefer the bottle, so if you want to give it straight from the tap, the baby might refuse, then you HAVE to pump.
- Breastfeeding should not necessarily be a tool for weight loss. If you don't eat enough, you suffer in the long run by depleating your body of nutrients because the baby takes what it needs and then leaves you with what is left. It could lead to vitamin and mineral deficiencies and that actually will make it more difficult to lose weight.

Anyway, I hope that answers your questions!