My baby is 6+ months old and has grown so fast that he's already pushing the limits on 9-12 month clothes.
Some things he gets hardly a wear out of at all before they are too small. I don't buy a lot, he only has one drawer of clothes which is about half full.
What would say would be the basic clothing requirements for a non walking 6-8 month old that will be wearing 12-18month clothes.