I'm still breastfeeding and I plan to do so for a long time...
About the calories needed for breastfeeding I heard that it's about 300-400 calories a day... but maybe it could be from different sources and I also heard that the longer you feed your baby better are the chances that you lose extra weight...
It is also recommended that when you're breastfeeding you don't lose more than 5 pounds a month because you don't want all the bad things stored in your body fat in your milk (exept for the first weeks where you loose really fast)