M.M.
How long do you plan on BFing? Early introduction to foods can lead to early weaning. I would recommend taking it VERY slowly until at least 6 months. Babies don't even need food until 1 yr. Here's a great site...
http://www.kellymom.com/nutrition/solids/
Also, don't worry too much about the rice cereal. My little guy never ate it. It doesn't even really HAVE to be their 1st food. But if she will eat it, go ahead, since it's good to get her used to grains. But you still need to be breastfeeding LOTS. That is where she will get most of her nutrients. Food at this point is just "icing on the nutrient cake". : )