One thing I've run into with girls clothes is "outfit" mania. With boys, it seems like you can mix and match separates. With girls, it's all about the "outfit" so matching shirt and pants or jumper. I'm trying to move away from this, but it's hard when we get so many outfits like this as hand-me-downs. It really adds to laundry and limits her wardrobe flexibility.
Anyway, dd was born in late september, and I dressed her mostly in 1-piece suits until about March. We keep our house pretty cold in the winter, so it was easiest and warmest to just keep her in pjs/blanket sleepers all day. So, I had about 5 pjs and 4 blanket sleepers, in 3-6 month size. I usually put an undershirt onesie on her as well. Then I had maybe 2 dress up outfits, for special occasions. And then maybe 2-3 daytime outfits, for playdates or classes out of the house (where she'd look silly in pjs). I also had a fleece bunting for her, for outdoors.
Seems like I never had enough warm sweaters or light cotton hats for my winter baby. Keep these!
Now, for spring/summer, she's wearing mostly pants/leggings and short sleeve or long sleeve shirts. I also bought her a few sundresses, because they're cute, and the diaper covers that come with dresses can double as shorts. So, she has about 4 pairs of pants/leggings in 12-month size, plus about 6 short-sleeve shirts, 3 long-sleeve shirts, 3 light sweaters, 3 pairs of shorts, 3 swimsuits, 3 sun hats, 3 sundresses with diaper covers. I'm trying to stick with a light pink/white-based palate, so all the tops and bottoms are interchangeable. For pjs, she's now wearing her big brother's hand-me-downs, in 12-month size. I'm hoping this will get us through to fall!
Sorry this is so diffuse--hope it helps somewhat!