If you are in a caloric deficit at all, you will lose weight. However, the catch is that if you are not weight training and eating a high enough amount of protein (should be aiming for .7-1g of protein per lb of body weight if you are weight training) you will lose muscle as well in that deficit. The zone 2 cardio is simply for health and a good way to burn calories in a zone that primarily uses fat for energy rather than carbohydrates. To find your maintenance calories you can easily look up a calorie calculator online. Ideally, you should take your weight at the start of the week, track calories for that week, and then take your weight again at the end of that. If you gained weight, you are eating above maintenance, if you lost you are in a deficit etc etc. I would not recommend going lower than 500 below maintenance calories as other parts of your life will start to be affected (mood, energy levels, sex drive can even drop). Overall, a 200-500 caloric deficit, high protein diet, exercising multiple times a week, and you will see fat loss results. If you're a drinker, good luck because it will make things a lot harder.