Hi and welcome!! I've never had children but what I hear from friends and reading, the baby gets what you eat and the core definitely has more nutritional values
Plus, yes, you get to eat more, which I also hear is very important
seriously though, with Core and BF'ing alone, the weight will just drop off since BF'ing is so great at helping burn weight. BF'ing alone burns 200-500 calories a day according to the experts...not my friends but the internet "experts"