My ds was 7-4, 21" at birth, and the 0-3 stuff swallowed him at first, but he bulked up really quickly. The couple of newborn outfits we had lasted *maybe* 2 weeks.
I second the recommendation for gowns. We

gowns with DS and have a good stash going for this guy. They're easy to put on, easy to diaper around, and you can either pull them down to keep baby warm, or pull them up to let them kick.
You might want a cute newborn outfit or 2 if you have someplace you have to go when the baby is tiny...like a christening, bris, naming, whatever, but I'd stick to 0-3 outfits and gowns, IMO.
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