Self defense generally provides that you can use an amount of force that is equivalent to the threat you are facing. For example, if someone is threatening to punch you, you cannot shoot them as your use of force is greater than the threat.
As to the gun, we will need a Florida attorney to tell us whether the legality of the possession removes the right to self defense. That is different from state to state. Georgia does not allow convicted felons who use a firearm to defend themselves to use self defense unless the firearm was possessed after the threat (think of grabbing your friend’s gun after being threatened).
But I would remind everyone to be slow to argue self defense or otherwise. A newspaper article will be 1/100 of all the facts in this case that a jury will hear.