You will definitely need some 0-3 as well, and depending on how big baby is you may need some newborn. My son was born at 10.7 and still wore 0-3 for a month or 2, he never fit into new born. But if you have a 6 pound baby they may wear newborn for a couple of months. Some babies grow quite slowly, some incredibly quickly. My son was 26 pounds and in 18-24 month clothing at a year old, he never wore the same size for more then a couple months. So far for this pregnancy I plan to have about 5 newborn sleepers and 1 or 2 cute outfits. About 7 0-3 sleepers and a couple outfits (I don't bother with much other then sleepers early on). 3-6 about 7 sleepers but definitely more outfits starting then, as they start to become Mobil and more active. If your planning on having a baby shower you will probably have more then enough stuff, happy shopping
Every baby is different so its hard to say :/
My baby boy weighed six lbs when we left the hospital. He wore newborn clothes for a month. He now wears 30-63 month clothing and hes two months old. Some babies grow quicker than others. I would definitely buy at least two or three newborn outfits and a bunch of 30-63 or 0-6. Night gowns that are big (0-9) are the best!! They will last a long time and they're easy for diaper changing in the middle of the night because all you have to do is pull them up and down