Answers: I don't know about a must, but its a good idea because anasthesia can make some people vomit, and if your lying on your back unconscious it is easy to aspirate stomach acid into the lungs which can kill you.
yes, because they give medicines that can paralyze your breathing muscles. (they also have medicines that reverse that effect within like 2 seconds)
Not necessarily. Some can be done with local or area blocks. C-Sections are routinely done with either an epidural or spinal anesthesia and only some O2 by mask or nasal cannula is used.
Here is more information on technics of intubation.
How else will ya breath when your lungs are paralyzed ..
It depends on what you define as "major surgery". If the procedure calls for general anesthesia, then paralytic drugs are usually given. If this is done, you must be intubated or else you will die of suffocation, you can't inflate your lungs. Also, the inflatable cuff around the outside of the endotracheal tube prevents the accidental entry of foreign substances or fluids into the lungs.
it always happens on tv.
major surgery yes, minor surgery no.
To my knowledge it is only required when the patient is under general anesthetic thus the lungs might be too relaxed or the patient might go into anaphalactic shock (allergic reaction) to the medication.