I'd just buy 1 box of nb size, or maybe 1 box each of 2 different brands. You don't want to stock up and then your baby has a skin reaction or something and you need to switch brands.
2 boxes each size
Babies use newborn probably a month my son was ( 7 pounds) they use alot of number 2 diapers and number 3 diapers
If you live near a shop then just buy some 1s and 2s, and a short trip out will be good for you when you run out :)