RE: Muscle mass and cardio
OK... cardio and catabolysis differs for each and every person.... the numerous Origin test results have shown that. As a good rule of thumb you should keep plenty of low intensity cardio in your week - walking is fine as it tends to burn fewer carb calories and more bodyfat calories. HIIT done once or twice a week is also very good but ensure that you take whey protein before and after the session to minimise catabolysis. HIIT in itself burns a fair few calories but the main advantage is the longer elevated metabolic rate it provides.
If you combine this low intensity exercise with a decent diet which is high in protein, moderate in Complex carbs , very low in simple carbs, and moderate to low in good fats then your fat loss will be massively improved.
Jogging will burn more bodyfat as a percentage of calories it uses than running as it's lower intensity and can be conducted for longer duration. Fat for energy is a very sustainable process in the body and is good when the body doesn't need massive amounts of instant fuel as the process for the body of converting fat for energy is much more inefficient than converting carbohydrate into glycogen energy (this is why long duration low intensity exercise is good for the bodybuilder wanting to lose fat IMHO). So when your body wants a lot of energy fast it looks for carbohydrate. If it can't find glycogen in the muscles then it starts the catabolic process of converting protein to fuel (IIRC this gluconeogenesis).