10-15 percent of your daily calories should come from protein. As a general rule, to determine daily protein intake multiply 1.5g x desired body weight. Divide that number by however many meals you eat each day and that gives your protein intake per meal. If you are trying to gain muscle you can multiply the desired weight by 2g or if attempting to lose muscle you can reduce it to 1g. For instance, a 200 lb person who wants to be 150lbs would do 1.5g x 150= 225g daily. If they eat 5 meals per day that would be 45g of protein with each meal.     

The theory with empty stomach cardio is that your body is coming off of a fasting state, has low insulin levels, and immediately burns fat. The problem is that depending on the intensity level of cardio you may not have enough energy for the duration of the session. You may also find strength training difficult due to lack of energy. Additionally, there is no guarantee that your body is actually burning fat simply because your sugar levels are low.

Six pack abs start in the kitchen, not in the gym. You can do every variation of crunches and sit ups, but as long as there is fat covering your abs, the six pack will never show. The key to a great looking set of abs is balanced nutrition paired with exercises that target various dimensions of your abdominal muscles.