Stars of merit:
You get a box with stars for each sidequest, and for completing the main battle, so you do better on epic battles with 3 sidequests than you do on epic battles with two sidequests.
Epic battle main quests and sidequests are "dailies" -- you can run the same epic battle twice in one day, but you won't get the box of stars for the main quest the second time through, and if you get the same sidequest, you won't get the box the second time (though I think you still get the skirmish marks for them?). It can be somewhat worthwhile if you get different sidequests on the second run, but since you can't control that, you will get a far better return on your time in general by running a different epic battle the second time.
Stars of merit are account-bound; you can run your alts through epic battles to farm them (all you need is level 10, and you can run in duo mode partnering your low level with someone else's experienced person...). I've found that my low level alts appear to get more jewelery and fewer stars out of their epic battle boxes; I'm not 100% sure if this is a general rule or just luck, since I haven't run all that many times with low level characters so far. Low level people will get level appropriate items, so don't use them to farm epic battles for lvl 100 first age symbols!
DA class specific armor:
To get a piece, you need to do a set of landscape quests (which you get from a guy in the plaza in DA[1]), and a set of six quests within the training instance. You will learn to hate the training instance, because it is a daily, and each day you pick one faction and are given two randomly selected quests from the six possibilities of that faction. So, if the random number generator hates you, you will spend day after day on a faction getting quests you've already run -- this will give you a nice pile of gold tokens and the tokens you need to hand in for the armor, so the time isn't totally wasted, but after the tenth time trying to get that one last quest, you will want to throw your computer out the window. Also, check the factions; one of them unlocks second age symbols rather than armor piece, which may or may not be useful to you (as those are getting pretty cheap these days), so you may be able to skip that faction. Since the tokens are transferrable, if you have more than you need from one faction, trade them with people to get the initial favor with factions or enough to trade in for armor if necessary
One of the faction's landscape quests takes you into Tarlang's Crown, which is nominally a "group" area; I was able to do the faction quests running duo with someone and being careful... you may be able to solo them if you are sufficiently good and/or careful.
[1]: one of the guys gives you a single quest to go to Tol Aduial and kill drakes, and you'll get the rest of his set of quests once you get there, so be ready to get more quests on the island.
If you want to do slotted armor, you can skip the whole grind here, and do an entirely different grind! With the best essences and some thinking about what works for your class, slotted armor can be better than the DA armorset (or a combination can be better; for some classes you may want two pieces of the DA set for a 2-piece set bonus and then go slotted). But... Getting supreme essences is a royal pain! Grind grind grind for random drops, then try to craft them and hope they crit. There are guides elsewhere on the forum for getting the most out of slotted armor