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
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