Hi @dixiegal- thanks for the interest! Dark or medium brown is a great color to start with, because it's easier to see. I am in the process of making some more in yearling and kid-- I just finished some in adult. Kid is the very finest, yearling is middle, and adult is thickest. I'm a fan of yearling myself, because it's a bit easier to grab with the needle and to see than kid. Whether you order kid or yearling, I'll be happy to send you a sample of the other so you can try it out!
One package (.50oz for $30) should be plenty. You could probably get away with .25oz, but it would be a shame to run out in the middle. Color can vary a bit from batch to batch, so it's best to get everything you need for a baby at the same time. When the hair is long, you can also get away with cutting it in half before rooting so you have twice as much. Just make sure to keep track of which end is the "cut end" (the part closest to the goat's skin). That's the end that you want to poke into the vinyl. If you mix up the direction the hair goes in, it can tangle more easily.
So...personally I root very sparsely and cut the hair in half, and I can easily do a baby with .25oz. If you prefer a thicker head of hair though, go for the .50oz. If anyone else would like to chime in, please do!