I washed everything. I had about 10 NB outfits/sleepers and the same in 0-3. I have a lot of 3 month clothing, but she will be in them a bit longer than the other sizes.
I go through 1-2 two clothing changes a day. The only time I change her is when there is a blow out or a large amount of spit up. DD has reflux so she spits up frequently. I use bibs to keep her clothes clean/dry. I don't like laundry.
DD was little at birth, 6.5 lbs so we were in Carter's NB clothes for the first 6 weeks (Gerber clothes run way small) Since then she's been right around 50% percentile for height and weight so she's closely corresponded closely to the age range on the clothes. If your LO is expected to be over 8 lbs, I might just skip the NB clothes all together except for 1 coming home outfit. Otherwise the first few months we pretty much lived in the staples: onesies and footed sleepers. With 6-8 sleepers and ~10 onesies, I did laundry 2-3 times a week. DD wasn't much of a spitter upper in the first few months and we rarely had blowouts so she stayed pretty clean and dry most of the time.
I would just wash the 0-3 clothes now and have just a few NB ready to go. One thing I'm just realizing is that they just grow so quickly from 1-6 months that I would not stock up on too many of those sizes. Plus take a look at the size of the clothes and don't assume that those numbers are absolute as some brands run small.
I washed everything and should not have. It's all just so cute when you're prepping for a new LO. NB I didn't have much of since I didn't register for any. I think I had a pack of sleepers and onesies. Even 0-3 she wasn't in the sleepers very long, she was a tall baby. I only ever went though 1-2 outfits a day. She wasn't a spitter, and I used bibs when feeding to keep the formula off of her.
Also, what other people like you may not. A friend of mine gave me a ton of the gowns w/ elastic at the bottom, she loved them. I could not stand them, they ended up around her chest when she was sleeping.