For AS, you only have to be adjacent.
DFA does not require you be on the target, as that's physically impossible. Not going to require you to stack miniatures on top of each other.
Any adjacent hex that the attacker can move to is fine. Attacker moves the unit, attacker makes the decision as long as it's a legal move (can't move behind the unit if you don't have enough movement to get there). Defender doesn't choose anything about the attacker's movement.
Charges and DFA have to be in base to base contact. For hex play, that means adjacent hex and at same elevation. So in your example, they could not do a charge or DFA from a level 1 hex against a level 0 target.
Target Numbers look correct.