Self defense questions

There have been several incidents in the news lately where the initiator of a physical struggle has been injured or killed and/or third parties injured. This creates a whole series of questions about self-defense that have been addressed in law may deserve to be revisited.
Edit to add> I am not so much asked what the law is but what it should be

Assuming an unprovoked physical assault:
-is there a right to self-defense?
it has been suggested that "it is better to be a victim than to risk escalating situation"
-is there a right to use lethal force?
can a victim defend themself proportionally if the assault has the potential to cause serious bodily harm
-does lethal force include the use of a firearm?
may the victim use a knife, baseball bat, car, any other improvised weapon but not a firearm due to the greater risk of lethal injury

The answers to those lead to two additional questions:
-If the answer to any of the above is no, at what point does the victim become responsible for the wellbeing of their assailant?
essentially at what point does the paradigm reverse and the assailant becomes the victim
-Even if all of the above are answered yes, who is responsible for any injuries to third parties?
will the assailant always be responsible for any injuries as those injuries would never have occurred without their illegal action, or may the victim take on responsibility even though the injury to a third party was done inadvertently while protecting themself

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