Just be careful of getting too transactional. Because, the day your son figures out other places to get goodies besides from you, you may lose your leverage over him.  But yes, you absolutely must communicate that he is not the King of the Universe. That is VERY Jewish. Will you pulleeeeeese get religious? That codifies and conveys that principle better than you can, unless you feel competent to re-write civilization from scratch. Who has time?

People's heads are serious. A head injury, no matter how minor, is never minor. You seem awfully blasé about an object striking someone else's child's head. Biting is absolutely bestial, and must never be allowed as an emotional expression, at any age at all, OK?

Your touching admission that you didn't follow through, and punished randomly, creating an anarchical world, a Hell, for your understandably enraged child, is honest. So, now you will be consistent. Not geniuses, just CLEAR on what you think and feel, and consistent. You must not allow him to become disgusting or annoying to YOU. You would be doing him no favors! You must keep at him, until he is someone you like and accept, and who others will find OK, also. Soon. There is nothing meaner than allowing someone to grow up an unbearable person! One always has to be thinking, thinking, thinking, and ahead of the game.