534243 OSC Checkout Process change.

I have a osc website that is fully working. I need a very good coder to move the discount code field to the 2nd stage. At the moment, the discount code field is located within the cart. But at this stage, the cart does not know what the shipping cost is because the delivery address is selected in the next step. So I want to move the discount code field to the 2nd stage where customers select the shipping address. So that if I input free shipping coupon code, it discounts according to the delivery address. Please ONLY BID if you are a code expert and have good experience. I don't want programmers that create bugs everywhere after fixing one.