The way you are doing it right now is the best way to burn fat but not necessarily the best way to build muscle. If your goal is to burn fat, then keep doing what your doing, if your goal is to build muscle, then you'll achieve better results if you do your cardio following your workout, or even better, on a totally seperate time. Also, keep in mind to eat eat eat if you want to build muscle. You may have heard this, but make sure your getting at least 1 gram of protein per pound, if you want to gain muscle weight.
Also, about the body fat thing. Keep in mind, a healthy body fat percentage for males is about 12-15% for females, 18-23%. I would not reccomend going below those ranges. Your body needs fat and uses it as a source of energy. My body fat is about 11% and my abs show just fine. I don't even hardly do any abs exercises, they just sort of showed up on their own.
muscle definition comes from dieting or cutting down food volume and increased workouts either weights or running
