Before we talk about how much cardio you should do, you should at least know why it's so important.
Cardiovascular exercise simply means that you're involved in an activity that raises your heart rate to a level where you're working, but can still talk. Here's why cardio is so important:
Bottom line: you need cardio if you want to get your weight under control and get your stress to a tolerable level.
You say you have a 30 - 45min window of opportunity to take protein, etc. after working out. Does this mean 30 - 45mins after a complete workout, or does this mean 30 - 45min after working out a single muscle group?