1) If you're hungry, eat. If you're not... don't.
2) Calcium is found in a lot of things, but I find the easiest sources are spinach, broccoli, onions and carrots (http://www.citracal.com/calcium/foods/vegetables.aspx)
3) If you eat according to the PB, you won't have to worry about spiking insulin. That usually happens when you eat sugar, starches, and processed grains.
Figure out how much fruit is in the shake. You really want to limit fruit intake especially for weight loss.
Regarding Ca supplements, I've read that they don't really do anything if your Vitamin D is low. I'm sure there are others on here who could elaborate, but here's a good link on the subject: