I've also started using the dailyplate to track my calories and fitness and really like it. I lost 45lbs without officially tracking by just exercising and eating better/less junk and keeping tabs on my portions. But now that I'm down to the final twenty, I'm finding this very helpful for planning my meals. For breastfeeding, I just picked my activity level and then bumped up one for breastfeeding. That gives me 300 extra calories, which seems about right. But I'm nursing a toddler not an infant so you may want even more cals if you're nursing a baby exclusively. When I was nursing an infant and not tracking, I tried to keep my calories to 1,800-2,000 and was losing 1.5-2lbs/week. Now I try to eat closer to 1650 and am losing about 1.5lbs week (actually I tend to eat closer to 2,000 on avg and still lose this. Btw, these are all "net" calories after exercise - eg., if I burn 300 cals working out then I'll eat 300 cals more. I think while breastfeeding is a great time to try to lose weight more gradually and with a higher calorie count because your body is using more of those calories - so that keeps your metabolism going so that when you stop breastfeeding you pretty much keep eating what you were while losing weight but it's plenty. The goal is to end up being able to eat about 2,000 cals a day to maintain your weight (but if you're breastfeeding, you can eat that or a little less and lose). If you breastfeed for 1-2 years then that gives you plenty of time to lose the weight gradually and adopt a new lifestyle.
In terms of what to eat/what's healthy: I go for lots of protein and healthy fats, modest amounts of whole grains, lots of vegetables and some fruit with moderate "treats" worked in in smaller portions (e.g., alcohol, chocolate, baked goods, sugary foods, etc).