Self-defense is an affirmative defense - you have to raise it. This will come down to how your attorney defends your case. It should be raised absolutely. Whether the jury accepts it is the trick of the trade.
Basically, you can use non-deadly force to defend yourself from immanent use of non-deadly force against you to defend yourself. Typically, this would be the minimum amount of force necessary to prevent the harm happening to you. Your attorney will have to convince the jury that this is what you did.
This is too broad a question. It would depend on many factors:
How much force was used and was it reasonable force, etc. There are too many factors involved in something like this to determine self defense. Questions like this cannot be answered with a simple yes or no.
For self-defense to work for you you must not have escalated the violence. Many people will think that a push does not merit a punch in the face. You need to consult an IA lawyer.