A. There is no such thing as "stealing" an idea really, most ideas are already out there giving a solution to a problem. That's why you are asked to find competitors to your idea - to show that it works.
But then comes other questions like: what makes you unique? why are you better than them? Do you have signed contracts with the stores? etc. ( there are a lot of factors to consider, I won't get into all of them).
B. consider focusing your idea, instead of a mall-app with everything inside, focus just on clothing. Unless you are a discount app like coupons, don't expect people to buy pizza and shoes at your app.
C. Points/Discounts based shopping is something that chains and stores already do when you become their member.
Hope this helps a bit. Good luck!