I would suggest the following plugins, bro:
1. ThirstyAffiliates (+ all their add-ons)
2. WP Coupons
3. Bitly (Use a custom domain name for this!)
4. WP Rich Snippets or Schema Ninja
5. EasyAzon (If you are into Amazon Associates.)
I'm not sure about any free WordPress themes bro but do check out ThemeForest, you'll find plenty of Affiliate related themes there. Let us know if you have any more queries, please.