I think the perfect collection consists of a good ring sling and/or a pouch, a structured or unstructured ABC/soft pack carrier, and a wrap. To extend past that I would add a summer/shower sling and a winter sling. So, out of all of those the only thing you're missing is a wrap! And for a newborn, I highly recommend a knit wrap like the Hug-a-Bub or the Moby Wrap.
Magical Mama, joyfully home educating my three wonders: FR (12/02), EG (05/05), DK (06/09)