What happens when you copy an Epic spell?
Copies made of the original spell by Echo Mage have the epic keyword, and so you do get multiple dominions/turn after.
Copies made by the epic trigger do not have the epic keyword.  So, the answer to your second question is that Echo Mage copies of those copies are "non-Epic."


Here's the salient rule that addresses why answer 2 is different from answer 1.


  702.49a Epic represents two spell abilities, one of which creates a delayed triggered ability. “Epic” means “For the rest of the game, you can’t cast spells,” and “At the beginning of each of your upkeeps for the rest of the game, copy this spell except for its epic ability. If the spell has any targets, you may choose new targets for the copy.” See rule 706.10.