Which are some affiliate program for USA like cuelinks where all merchant can be found.
Shareasale.com and Clickbank is what I use and there offers from USA and other countries to promote.
Clickbank and commisionjunction aka CJ are the best..
Not a good decision. Over 95% search results are occupied by RetailMeNot. If you are not good at finding low competition keywords, you will have hard time ranking your coupon site.