Part of being any kind of artist is trying different techniques and seeing what works for you. Everyone develops their own favorite colors and ways to apply them. And that’s just the beginning! There are lots of people on here who are willing to help, but there is no right or wrong way to do this.
Creating beautiful dolls is fun, but you are going to have to figure out a lot of what you want to do on your own.
YouTube has some good videos where you can see what other people do as they paint a reborn, but no one can tell you exactly what to do to get a baby to look the way you think a baby should look to be realistic.
BB sells test limbs and they very often have kits on sale for low prices. Maybe you could get one and try different colors and different sponges and see what looks good to you?