what are the laws regarding self defense with a gun?

It's not clear what your question is. You state your understanding of the law and then ask what are the circumstances. I don't know: you tell us.

Respectfully, the defense you are asking about requires fact specific circumstances to determine the applicability of the defense. The circumstances under which it may apply are numerous, and therefore you would need to repost this inquiry with additional facts to determine the applicability of the defense. Good luck.

DISCLAIMER
I do not practice law in your State. This answer is provided solely for informational purposes only. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising.

Each situation is fact specific and the current case law on it is mixed. Generally, you do not have to retreat, and may use deadly force against an attacker, if you are in your car or home and the attacker entered the home or car forcibly and unlawfully. You are better off to use great caution before using deadly force when it is not necessary to do so, no matter where you are.

Outside the home or car, you are only entitled to use deadly force when you are in a place you are entitled to be and deadly force is being used against you or another person.

Unless you are in your car or home, you can only use deadly force to counter deadly force. If someone is unarmed, you cannot use a baseball bat, knife, gun, etc. to hurt them. I think some people carry concealed weapons, which is usually illegal, hoping they get attacked. That is why you have to have a permit/license to carry a gun. This from FL Dept. of Agriculture and Consumer services division of licensing talking about self-defense and deadly force.

http://licgweb.doacs.state.fl.us/weapons/self_defense.html