i had 5 newborn cotton bottoms wraps, and that worked well for us. we would have 2 to use, 2 in the drawer (for the next day) and one spare in case of a poo. Molly didnt poo loads but there were days when all 5 wraps got pooed on! although we also had a small fleece wrap and 2 pockets that could be used in such an emergency!!
i have 10 new, newborn CB wraps that i bought thinking i could use them for the next baby, but i will most likely use wool or the dozens of pockets lol!
so yeah, you should get at least 5 newborn/small size, but theres always room for more!!