Her dress is actually quite simple (I'm assuming you're going with the standard dark one). First, some questions:
What's your sewing experience?
Is there a place nearby that sells patterns (like Fabricland, Walmart, Joann's)?
Do you know how to work with patterns? How to alter them?
I would recommend Simplicity pattern 2586 style C. You can make the skirt and sleeves a little wider and fuller.
For the dress fabric, look around your local fabric store for something that has a nice drape to it (as in, when you hang it over the edge of something, it hangs as opposed to creasing or wrinkling awkwardly). Nothing shiny! The bow fabric would have to be a little stiffer to maintain its shape. I would buy a red headband to stick the bow to.
Her hair could be either dark brown or black. Are you planning on using your own hair? Cosworx here has a fabulous selection of wigs to choose from, like this one:
(imagine it in black)
Contacts aren't necessary. I find that unless the character has strikingly noticeable eyes (like Harry Potter's green eyes or Sasuke's red eyes), then maybe, but I don't think you have to worry about Kiki's.