Organizing Clothes

We have received a lot of hand me downs from my nieces, ranging from newborn to 6T. I’m trying to organize them and planning out the best way to do so. I’m a FTM so not sure my idea of what’s best will actually be what works best.

So I’m looking for opinions.

1. What size range should I keep out of storage and accessible. At first I was considering keeping up to 12 months out but now I’m thinking that may be too much.

2. For everything I’m storing, I plan to store in size groups so when it’s time to graduate to another size it’s organized and easy to do so.

What sizes would be recommended to group together?