missed field goal from own end zone is a safety?

I see your point: in general, on a missed field goal, the ball goes over to the other team where the ball was kicked from. So ... what happens if the ball was kicked from inside your own end zone?

I don't know the answer. There may not be an answer. It doesn't make sense to attempt a 111-yard field goal.

Yes, if the defending team causes the ball to become dead in the offense's end zone.

Any coach who tried that should be fired. If the line of scrimmage is so near the end zone that the kicker is standing in the end zone, punt the damned thing.