I posted this under Q & A, and though I can edit the post, I can't delete it from there. I just think it's probably a better question for the community because I assume these scenarios have come up for others.

My client is a book publisher/online book retailer. I need to extend the commerce coupon functionality by adding two additional fields to the percentage discount coupon. Besides the percentage off field, I need to be able to offer free shipping with a coupon. I also need to be able to limit the discount to specific items.

Examples:

Scenario 1: Blanket 10% across the board on all products (default percentage discount coupon functionality)
Scenario 2: Blanket 10% across the board on all products + free shipping
Scenario 3: 15% on products that are published by the client (tracked using a CCK field)

Create new rule, have multiple rules, modify existing rule? Any pointers, tutorials, links, ideas, etc. are appreciated.