Epic Level feats work this way:
You get feats every 3 levels, just like you did in levels 1-20. Those come at levels 21,24,27. You can pick from the heroic feat list or from the Epic Feat list. The Epic feats may be available at 21 or 24 or 27, depending on the feat. You can see a list of the epic feats and their requirements here:
http://ddowiki.com/page/Epic_FeatsYou will also get epic destiny feats at level 26 and 28. These feats are different from the traditional heroic/epic feats. You cannot select from the traditional feat lists for these two feats. You must pick from the Epic Destiny Feat lists. (This is where you find Epic Arcane Blast, for example). A complete list is here:
http://ddowiki.com/page/Epic_Destiny_FeatsEach feat is linked to a destiny sphere (Arcane, divine, primal, martial) and has a "Destinies capped" requirement of 1 or 2. Some feats equire 1 capped destiny in a sphere. Some require 2 capped destinies in a sphere. So, to access Epic Arcane Blast with your level 26 feat you must have earned the full 1,980,000 xp in one of the 3 arcane epic destinies (Fate Singer, Magister, or Draconic).
It has nothing to do with whether or not you ETR. It only has to do with whether you have capped any epic destinies yet. This can be an issue for a new character as you might spend your first life just "unlocking" destinies. You only need to go to level 3 to change destinies to another destiny in your current sphere or to level 4 to access a destiny in an adjacent sphere. That will give you more fate points more quickly and allow you to have more twists, which are great. But it might mean that you don't have access to any epic destiny feats if you haven't capped at least one destiny by the time you get to level 26. (Level 26 is 4 million XP or so, and you need 2 million to cap a destiny, so you shouldn't have a problem but you do have to do some planning). This is usually only a problem that first life as you end up with multiple capped destines by the time you have completed your 2nd life, easily.