If ball is fumbled out of end zone?

Depending on which side recovers the loose ball. If the defense player does it is a safety and worth 2 points to that team and they get the ball back on a kick off. If the offensive player gets it,...

From the front of both endzones, it's 100 yards.

100 but both end zones are 10 so from very end to very end it is 120

If the QB fumbles the ball out of his own end zone it is a safety.

No