I would only wash maybe one newborn onzie as I've heard some babies never wear NB. For my son, I bought 4 more newborn onzies, which he only ended up wearing a week....BUT I washed them so many times in that week b/c at that stage the diaper leaks so much. Make sure you have the snap undershirts (Carters and Gerbers make them) as you may need to dress around the umbilical cord stump. Also, the cotton baby stuff seem to shrink a lot. I ended up putting them in the dryer for 10 min and hang drying after that. I also dressed him in 3 months, eventhough they were big in the begining and layered a snap undershirt and pants under it (rolling the pants so it didn't touch and irritate the umbilical cord stump). Make sure you have lots of socks. Sleepsacks are also good in the house (fyi..you can often find them in TJmaxx & Marshalls for a lot cheaper than the baby stores). My son hated swadding, so we used them at night. Carters was the only brand I found with long sleeve ones adn they make them in 0-9 months, so they are prob too big for a newborn, but in a month or 2 they might be used.
My son was born in May and I am now expecting in Jan. The baby hats we had didn't stay on very well (stuff like the carters ones that come in a 3 pack or that come w/pj's- very light). I have been reading up on winter hats and it seems like the bundle me hat in 0-3 months is good option, although some reviews say its very small.