Combat
Yes.
A character can use a Combat Maneuver or Power to force another character off a ledge. This must move the character into the space past the edge of the ledge. At that point both characters should roll a Reaction check. If the character that is being pushed off wins, they finish the move at the ledge, just dodging the fall. If the character that is pushing the other off wins, then the character falls. See the Athletics skill for details about falling.
The Reaction check is made whether it is a Move or Teleport with the results being the same.
This extra rule is in place to eliminate the ability to easily remove a character from game play. Everyone should be able to play Atomic all of the time. They might be at a disadvantage clinging to the cliff face 2 rounds down the ledge, but they are still in the game playing. This is much more fun. That is what the Atomic RPG System focuses on.
No it can not. You can only affect a target with a Power one time during a turn.
Example
A player character uses a power that can affect 4 targets within 4 spaces. There are only two targets within 4 spaces of the player character. Only these two targets can be affected. Each target will only be affected by the Power effects one time. They can not be affected twice due to the Power having more targets than can be hit at the time.
No.
Forcing another character into an obstacle does not cause damage. The Move would stop where the obstacle is.
However, an Advanced Atomic Power can have both a Move and Damage component.
Keep in mind that a character can only Move by means of its normal Movement type. A character that has Ground Movement can only move things by Ground Movement. The character cannot be Move something into the air. This would require the character had a Movement of Fly. A Power could be created to give the Movement type of Fly and then have a Move effect added to it.
When you use a Power with multiple targets you will make only one Attack roll. The result of the roll will be the Defense that your Attack hist. You will compare this number to the Defenses of the targets that you attacked. If the number is equal to or greater to Defense of the target then the Power will affect that target.
This method of determining hits and misses speeds a Atomic game up dramatically.
Example
A player character uses a Power that can has the ability to affect 3 targets. The player character rolls an Attack roll. The result of this roll is an 18. Now you compare this 18 to the targets Defenses. There are two with a defense of 15, which hit. The third targets defense is 22 which misses. This Power will affect 2 of the 3 targets.
Powers
No it can not. You can only affect a target with a Power one time during a turn.
Example
A player character uses a power that can affect 4 targets within 4 spaces. There are only two targets within 4 spaces of the player character. Only these two targets can be affected. Each target will only be affected by the Power effects one time. They can not be affected twice due to the Power having more targets than can be hit at the time.