In regards to duels look at the thread Channeler vs Channeler: FIGHT (no they aren't in the game ..... Yet.)

as for 2. in order

both auto-resolve and tactical battles are planned

yes

no data yet

squads / individuals (champions, magical beasts, channelers, etc)

3. basic naval warfare is planned 

Are battles still going to be turn-based?

Edit: Sorry. I should use the search feature to answer my question.  

Dueling is so World of Warcraft....

Dueling sounds more to Legend of the Five Rings to me... which sounds quite better than WoW (ignoring differences between a CCG/RPG and a MMORPG).

How so? Having played world of warcraft (and a ton of other MMOs) it didn't have a very deep dueling system (no MMO has in my opinion) but then again I always play on PvP servers. 

When I think of duels I think One on One battles followed by Starwars, Marvel Comics, and Boxing. I would love to see a dueling system used in Elemental.  

If sovereigns are so powerful then anything else besides a one on one duel will not do them justice.

Except for a Sauron-style mass butt-kicking.

And don't forget that Sauron's defeat required a sort of 'essence hoarder' (Gandalf--it had to take essence to come back from the Balrog fight, and it was late-game for him), a crew of champions (the Fellowship), *and* the mass armies that Gondor, Rohan, and the dwindling elves managed to field.

Another thing is if the sovereigns are so powerful and they are leading an army, does that army become unstoppable?

Not necessarily, I think I read on a gamespot preview that using your channeller in battle is risky because if your channeller dies, it was essentially game over.  So, even if your channeller was extremely powerful, there would be still be a risk of losing him/her in battle and getting knocked out from the game (I dont think Sauron expected to die fighting the Last Alliance).

Well, obviously it would depend. As has been said millions of times, channelers are only individual crazy-powerful if you hoard essence (which means you don't have many heroes or cities and haven't used many of the more powerful spells). This means that such a channeler will in all likelihood have a much smaller army than a channeler who focused his essence into things like champions and settlements. So a crazy powerful channeler leading an army attacking a player who didn't focus so much on his channeler will have to defeat a much larger army.

So no. A channeler leading an army wouldn't be unstoppable - because he would be stoppable by a larger army without a channeler, or a similar army also lead by a channeler - or an army lead by a number of powerful heroes. And, hopefully there will be other ways of countering such things, like by cutting off the army's supply, etcetera.

my wonder is will battles and dungeons use effectivly the same interface?  or will dungeons be like the overland map.

I'm not sure. I think that since the battle map owuld look like a single square of terrein blown up, it would have no inhomogenous features. Since a homogenous dungeon is generally not a good idea (Now we must explore the dreaded Square of Moria!!!!), I imagine they will be different.

I wonder if terrian will play a big role in battles. For example if your army is chargin from a hilltop do they get charge bonuses?

Depends on what you mean by terrein: we will likely get some kind of terrein bonus for specific units and trainings, but I think the actual map you battle on is going to be more or less homogenous (see above).