I named the littlest of my chicks last spring "Little." She's now the biggest. It's like calling the tallest kid in the class "Tiny." So I think Cupcake is a great name for your Brahma!
Use a warm wet paper towel to clean away the pasty butt crust. You may need to hold the paper towel on the crust to soften it up. Be gentle; their skin is very thin and fragile.
Cute chicks. Oh, so cute!