Clothes

La
How do I know when to say enough is enough with the clothes I'm buying? I didn't buy a lot of newborn stuff because I assume he might not even fit into it. I'm purchasing a lot of 0-3 and 3-6 month old stuff. Like 10 onesies each plus footie pajamas and some cute regular outfits which I suspect he won't wear very often. 
I mean, how many onesies should I buy for his first 3 months?