1# Solo sovereign gets full XP, 1 hero it gets 50%, 3 heroes 33%. It's up to you. If you split stacks and level your champions in the wild, you can "save" time that way. If you only care about 1 stack, you might as well put all heroes you care about in it as well. I usually just solo level at first, and add one of the high level champion recruits into my stack later. (Lvl 7 or lvl 9) The other champions get stuck on garrison duty to reduce unrest

#2 Have you considered slowing your speed in the start? Epic speed has more turns etc. than normal. But your tech speed will be slower of course.

#3 Dense! Monsters are supposed to be in the way!

#4 They are, but play with what you think is fun. That's what matters not what other people think. 

#5 The Master Quest? You win the game by completing it. Scroll down on the far left to see current quest status. The incomplete ones are usually on the bottom there. Clicking on them should give you the next path, or at least give you an inkling to in which area the next part is. 

Swarm will beat you down. But if you get that tectonic shield item that gives you immune to swarm, yes you are unbeatable

At least that is until you start playing Insane. Then the AI will spam that 10% accuracy tech over and over, so when you fight them, they all have 400+ accuracy and your dodge is useless....

1. I run my sovereign (fire mage) with Bacco as a bodyguard (axe, with cleave traits and heavy armour). They can clear out pretty much everything (especially if I get the ring of ash). Every other hero gets his or her own army. Preference is for troops with mobility, hit points and defense.

2. I've never come close to hitting the turn limit. 

3. Random, huge map, balanced type and wildland frequency, normal pace, plenty of quests, challenging monsters, dense monsters, magic and resources and more events. Opponents are set to hard, and usually 9 or 10 on a huge map to give me time to expand.

4. My sovereigns are 90% mages, 10% assassins. I tried the assassin dodge build and it's just so sickening. However, I like to melt things, so the fire mage is my first choice. I'm getting ready to try a warrior Sovereign with heavy emphasis on troops.

You have at least 2 options. A sovereign/hero casting imba spells behind your assassin dodge tank or some mage/archer units dealing the damage. Both of them can deal the damage necessary. If you expect the assassin to deal the damage as well you better be using Blood Rage (Death5) or Destiny's Gift (really late magic tech) to increase his attack and attack speed. 

How did you get your crit chance to 70? I max out at 59: Heartseeker, lucky skullcap, assassin's vambraces, whetstone, assassin bonus and lvl4 vital strike.

Looks like it was an exaggeration as I did not have the game in front of me.  I have only 53 crit.  Seems like it crits way more than that.

I fully admit that I have only played a few games of FE:LH at this point on Hard difficulty but I just don't get this love for mages and hate for assassins.  I've had good mages and no matter what, they need back up.  Maybe I'm not using my mages right but I get +spell dmg, -1 casting time,  and + fire dmg traits with the fire line + usually one other spell school (custom faction has magic books for sale) and my mages still dont come close to the sustained dmg output of my assassin.  I think my assassin went through the dragon gems quest where you have to fight three dragons together with 200-300 hp each in less than 7 moves (which isn't long at 34 initiative) without taking a bit of dmg.  153 dodge, 120 fire/lightning/ice resist, 75 spell resist, wraith touch hitting for 28 dmg, splash dmg crits (including counterattack splash dmg) hitting for 35+ dmg, 75% armor bypass.

Also, and I may be completely wrong here on how stack overall movement is decided, but because my assassin walks around by himself , he moves 6 times per turn and wears a compass so he he goes right over forests and swamps.  Because my mages need backup, they usually only move 2 times per turn. 

I even get more use out of warriors than mages for a majority of the game.  Warriors seem to do more sustained dps for me than mages for the early stages until about the point I get some tech to make better trained units.  I guess I'm also less inclined to cast spells because it is always fun to drop a volcano boost up some stats of your champions.

My assassin was running solo with about 95 dodge around level 8 and all I had to do was avoid heavy magic dmg. 

Wraith and lucky trait (+25% dodge) I guess. 

90+ dodge at level 8 is an outlier. My generous estimate below comes up to 80:

Skullcap 5 + Evade 10? + Wraith Blood 20 + Shield 10 + Dodge traits up to acrobat 17 + Skill Books 2 + Lucky trait 16  = 80

You'd need one amazing shield and several more skill books to pad this up to 90. Or there's a robe involved, too.

Anyways, an assassin with this kind of dodge is really going to shine. 

...But imagine what a lvl8 mage with lucky loot drops (spell staff, mage robes), the right enchantment (mantle of oceans) and hand-picked sovereign and faction traits could do...

1 & 4.
I play on Insane/Insane, and of all my runs, no class came close to the power level of the Assassin.  Nature's Cloak (Rank 1 Earth Enchantment) takes care of most of the magic damage.  I think I had her at 150 dodge around level 20.  I was taking down 900+ HP armies with just my sovereign.  Granted, you have to look at their accuracy before taking them on.  I went up against one army, and all the troops had over 200 accuracy.  Needless to say, I lost that one.  It's also good to have Air 3 so you can teleport (also, spells are affected by your crit chance/damage bonuses, so you can do some madd damage with that, too).  Air 4 for Cloud Walk is also good since the rest of your army probably can't handle AI armies until late game.

The third game I won on Insane was the first game I tried a dodge Assassin sovereign build (this is out of like, 50 games; I'm not actually that good).

A Beastlord Mage would be my second pick for most powerful sovereign.  When doing that, it's good to have a Commander champion in the army with for the accuracy/xp bonuses so your bears can one-shot things.  It's worth suffering the XP split for it.

2.
The turn limit is far enough off that you shouldn't ever hit it.

3.
Insane, Dense, Plenty, Many, Often, Epic (aka slow).  I like stuff happening. 

5.
There are, but they have sparse, outdated information.  I tried updating the fallen enchantress wiki a while ago, but after a few updates... It's a lot of work.  Forum is your best bet. 

Installing this mod may help you in future games:
http://fallenenchantress.nexusmods.com/mods/1876/? 

I admit I may not have fully explored the assassin. I never considered a 100+ dodge attainable, which it can be. I definitely noticed that the assassin can deal hella damage with weapons or spells. But non-critical hits suck, and early game, the assassin can really struggle without the right gear.

So maybe I'll try the assassin further, and maybe even change my tune...but for now, I'd still rather be a mage on insane/insane. And a mage can solo epic stacks, too (so can a warrior).

Maybe the Defender does need a taunt ability, which covers a certain area or all enemies, and all who don't resist automatically attack the Defender for the next 1-3 turns (depending on balance).  The Defender definitely needs some way to turn a battle.