1) Can a person use more than one coupon/gift certificate at the time of signup (enter more than one discount code at a time?)? 2) Also, what if the coupon/gift certificate dollar amount is larger than the subscription dollar amount? For example, the coupon is $20 off but product's price is $15. Hopefully it wouldn't ADD $5 to the customer's credit card, right? If the case is that the sales price is $0, is the remaining coupon/gift certificate dollar amount still available to the customer for future purchases (the customer would still have $5 left on coupon/gift certificate)?