When doing abs, you should worry about quality, not quantity. As far as the breathing, you want to exhale when you are pulling up. You should also keep your abs constricted at all times! Your arms should be out wide, so you shouldn't be able to see them in your vision. Also, act like there is a grapefruit underneath your chin.
Just to let you know, you will not get a 6-pack from doing just abs. You have to lose the fat around the core by doing cardio. You also have to watch your diet, you have to lower your fat intake. Don't waste your time by doing 200-400 crunches a day! Abs are just like very other muscle, they need time to repair, so only work them 2-4 days a week.
Good Luck and hang in there, it will take some time!
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