None, do some light calisthenics: Jumping jacks, air squats, little jump rope, little shadow boxing. Nothing high intensity, just get the heart rate up a bit for a couple of minutes.

"How to be a fighter without being a murderer ?" For starters don't get into fights. After that fights are chaos, you don't know what will happen.

This is what I have suggested to people in the pass, gotta move around them. When we would spare in our karate class I would often work with lower levels which tended to be much smaller than me. Getting into a punching match wasn't going to work. I would tell them move, get inside for a few good shots and then back out (unless you had a knockout shot available). If they wanted to stand and go toe to toe trading punches I was more than happy to do so with them.

Takedowns and kicks? Since the OP says "boxing" I am assuming the classic style of boxing, takedowns and leg kicks are not allowed.

Usually if someone chooses you as their target it was because they thought they could beat you, either through strength, age, experience, or some other factors (or combination of factors).

My style is called Okinawa Kenpo Karate Kobudo to indicate we also covered weapons.

I'll second Rory's book, or any of his books. All good stuff

12 ga shotgun with buckshot would do wonders in stopping such an attack

SPEAR: Spontaneous Protection Enabling Accelerated Response. Protective SPEAR is the act when you are attempting to push danger away from you, which tends to be a natural response. I will modify and not say any attack, you can't do an ECT drill against a sniper with a long range scope and high powered rifle, but talking physical attacks.

Ask a lawyer in the area where you live. IN general you can respond with equal amount of force in any given situation. That is general and there are exceptions.

Competitions will often have requirements for gloves. For sparring and heavy bag I use 16oz gloves, personal preference. For choosing the size, try them on and see how they feel. Try different weight of gloves.

I would agree with Fight Science and Human Weapon.

Practice and keep things simple. If a person has a dozen ways (just picking a number at random) to grab your wrist and you have a specific technique for escaping from each one then yes, choking is very likely. Don't over think, do.

Yup, their school, their rules. My previous karate school it was not uncommon for political talk with the head instructor before class started. Also talked about poker playing too,