Firstly, max out the intensity of your exercise(make it burn) and include something besides crunches like reverse crunches, hanging leg raises, or bicycle crunches. Leave little resting time in between.
As for the cardio to lose bodyfat...yes that will help you lose bodyfat but it would help a lot more if you ate carb heavy meals before and after your workout so that your muscles will be sensitive to the insulin(not your fat cells). Don't eat potatoes and milk if you're not going to be working out that day, you'll just get fatter.
So to recap...for rippling abs you're going to want to:
1. Work out like a champ, be a warrior; every time you workout push yourself.
2. Instead of running at a steady pace or other boring cardio, do some sprints. Your legs will be more powerful and you'll burn more fat.
3.get rid of all unnecessary foods like desert, candy, anything too sugary and eat real whole foods.
Somewhat. 300 crunches a day is definitely going to give you strong abs, but it isn't going to make you lose the fat on your stomach (I don't know how much there is right now, though). To lose fat, you're going to have to do cardio (running, biking, swimming, etc). If you get nice, strong abs without losing any body fat, then you'll probably end up looking even fatter, because you'll have more muscle underneath the fat. I would know, I'm guilty of it.
Holy crap that's a lot of crunches. Cardio is also really important when trying to get toned abs make sure you run or something. 300 crunches may get boring to you. I usually do a variety of exercises with one set of 50 for each. Try mixing it up with bicycles and such. Just google "ab workout" and there has to be a decent workout somewhere. Good Luck!
If you eat healthy, workout and do crunches every day, you will tone up. What you want is a toned stomach- which is sexy and athletic. A stomach that is flat with no tone is okay, but its not what you want to try for. Aim for toned.