0-3 month all you really end up using are snap-button onesies and zip-up or velcro swaddle things. You don't need many newborn diapers. They outgrow them VERY fast. Usually size 3 and 4 are most used diapers.

Also make sure to snag as many as you can of those waterproof cloth pad things from the hospital. Always stick one under the crib and wherever you change them. They're useful all the way thru potty training. Just slip one under the fitted sheet.