My kids went to catholic school so we are very experienced in the uniform thing lol.
girls all had 3 jumpers and or 3 skirts for older grades
5 short sleeved shirts and 2 long sleeved shirts.
1 pair of gym shorts
5 pair of socks
2 pair of tights
the jumpers can be worn for more than one day unless your little one is really really messy.
I recommend 7 tops and 7 bottoms. At that age (5/6), they still get really messy (playground dirt, glue & glitter, food from lunch, etc.) so you probably can’t wear an item more than once without washing.
By 2nd grade, you can probably get away with three sets.
That said, we have enough white polos for three weeks without laundry! LOL! This is because I bought 2 LS and 3 SS from Target and then saw a great deal at French Toast for 5 LS and 5 SS for the same price. I intended to return the Target ones, lost the receipt and they went on sale (so I’d only get the lower price back).