We warmed ours by putting it in a bowl with really hot water until the milk was warm. It worked out great! I don't recommend using the microwave, at least not for a while. I never heating his milk in the microwave until he was about 6 months old and I don't do it very often.
I've heard you should use warm/hot tap water to warm bottles. I asked my dr how much to feed also and he said to pump for about 10 to 15 minutes and to feed him as much as he is willing to take. Once he starts seeming uninterested to not force it.
i would always try to keep the milk at room temp and feed before it spoiled. in the summer it was fresh for about 5 hours. in the winter when my houses is cooler it lasted longer- up to 7 or 8 hrs during the day and 10-12 hours at night. expressed milk retains most of its beneficial compounds while it's still fresh. if you refridgerate it you can reheat it by submerging the bottle in warm water. a newborn most likely won't take it cold, but you can try. after it's reheated, swirl the bottle to mix the layers. there is research that indicates shaking breast milk breaks down some of it beneficial components.
http://www.justmommies.com/articles/breast-milk-storage.shtml has a nice chart showing storage guidelines.
as for how much to pump for a feed, in general the guidelines are to pump for 10-15 minutes. my baby generally took 2-3 ounces per feed in the first months, then 3-4 ounces per feed up til 6 months. babies take much less breast milk than formula, so don't rely on most feeding charts to tell you what to feed him.
Thanks everyone this has been very helpfull:)