Hi,
I think it depends on whether your baby is breast- or bottle fed. Breast babies tend to have dirty nappies more frequently. My one was bottle fed from birth and at most we used 8 nappies per day, but usually around 6. Both Huggies and Pampers absorb wetness incredibly well, so if your baby only has a wet nappy you really don't have to change more often than 4 - 6 hours.
I second the recommendation to buy bigger sizes, newborn and very young babies grow so quickly. I wouldn't stock more than 3 packs of size 1 and 2, and you're likely to get some at your baby shower anyway.