My 1st son was 7lbs 10oz so he didn't stay in newborn or size 1 for very long :)
I try and refrain from newborn diapers unless you know that your baby is really small. Newborn diapers only go up to 8lbs so I try to focus on size 2. I may get a couple boxes (big boxes) of size 1 but you should stay into size2 for a while so I try to focus more on those. You should plan on your newborn going thru about 8-10 diapers per day, good luck :)
Plan on 10-12 diapers a day. Most babies out grow newborn diapers around 3-4 weeks this of course is based of having 7-8 pound baby.
Size really depends on how big your baby is. I was told not to get many newborn size but now I regret listening to that! My son was 6lbs7oz and can fit preemies. After a week and a half of using NB we switched to premie size and will switch back to MB when he's a lil bigger.just remember to keep your receipt. You can always return or exchange the ones you don't use. (:
As for brand, so far Pampers have been my favorite. Huggies leaked on me and I really didn't like walmarts cheap brand, although I didn't really get to use them because the NB size swallowed my son.