Yes, you can do both, and the advice above is pretty spot on.
You can express breastmilk and give this to your baby from a bottle, or use formula.
I'm not sure whats advised in the us, but here when bottlefeeding it is based on your babies weight.
Up to 3 months its 5 oz for every 2.2lb, over 24 hours.
So divide this by the number of feeds your baby has.
So say your baby is 8lb, thats 40 oz in 24 hours. If you are feeding 10 times in one day, then its an average of 4 oz per feed.
If you're breastfeeding and want to use oral contraceptives, you would need to go on the minipill, which I think is progesterone only (its one or the other anyway!)
this will only be effective properly while you are breastfeeding at least 4 times in 24 hours.
Also, giving formula will impact on your breastmilk supply, as it fluctuates to a supply=demand, you if you're feeding less you'll make less milk.
I agree with the advice about waiting until your baby has a good attachment, although if you wait past around 6-8 weeks you might find that you have a baby who will not take to a bottle so easily.
I had a lot of problems with breastfeeding due to my son having poor attachemnt and a tongue tie and short tongue. It got a lot better at around 3 months and I wanted to give him expressed breastmilk from a bottle, but he refused to take it. I kept trying each day, but he kept refusing and continued to do so until he was 5.5 months old (note: I kept allowing him to breastfeed - if you only offer a bottle your baby will get hungry enough and eat!)
when you do use a bottle, the longer, cherry shaped teats are supposed to be best for infants who will also be breastfeeding, these are the king most hospitals will advise. (well, in australia anyway)
if you do a google search on 'la leche' you will find some good information on breastfeeding