Ether

If the copied spell divides damage or distributes counters among a number of targets, the division and number of targets can't be changed. If you choose new targets, you must choose the same number of targets.

The copy is created on the stack, so it's not "cast." Abilities that trigger when a player casts a spell won't trigger.

If the spell has any targets, the copy will have the same targets unless you choose new ones. You may change any number of the targets, including all of them or none of them. The new targets must be legal.

Ether's ability is a mana ability. It doesn't use the stack and can't be responded to.