You are right, there is serious info overload.  Have you read through the manual, the monster manual, the spell manual, etc.  Some dedicated players put these together and they are available on this site.  Specialize.  More specific to your questions; One thing that would help is to look at the special weapon types available to some domains. One has neat staffs that also add to dodge, making them harder to hit, and getting a hit back (counterattack).  One has access to horn bows, that are better than typical bows and don't need metal to make.  One has a bonus 'rush' move that gives the troop an additional move (not attack) with acool down of (I think 5) .  Some age automatic benefits to troops, like a double attack at -30 accuracy.  I'm still exploring all the nuances available, and sometimes getting slaughtered.  Some options will be controlled by resources.  No crystal = no magic arms and armor.  No metal = no armor beyond leather..  You get the idea.  For mid - late game units. mounting all troops is a big boon.  Warg riders get extra dodge.  (actually horse and warg get dodge bonuses - but warg is currently better for melee troops.   And horse/warg troops get movement bonuses on the tac map as well. remember that your mid game trained troops  will be better that even your most battle hardened veterans from the early game.  Bonuses to troops right out of a fortress with some of the buildings already built make them tougher.  Its sad to retire troops that campaigned with the sov for so many seasons.. alas.  And remember, Also, with several forts established, you hopefully built one on a two or three mana resource tile.  This is vital to later game troops.  When the fortress in training troops, cast battle spells on the fort - one adds a +1 fire attack to each figure you train there, for each essence in that settlement.  The +1 (or2,3) adds up really fast.  Its expensive at 100 mana to cast - but well worth it.  Other spells add to initiative, defense / per essence. This, coupled with the additional 'talents' given by virtue of the upgraded fort make the new troops quite effective when compared to the early troops trained out of need, anywhere.

BTW, I build mostly forts, and few towns / conclaves.  Why?  The settlements desperately need the garrison, and pluses to initiative - towns and conclaves are way too vulnerable in early game, and the salary costs too high to field sufficient troops to protect them all.  Most of these forts have no bonus troop buildings.  The added materials is also a big boon.

Sometimes, you find a sweet 3 essence tile.  While there are some benefits to building a conclave there - the needs of a highly effective military outweigh it.  Build your prime fortress there - grow it to size five, and enchant it with 3 spells that make troops trained there, well, magical.  My late game troops are always new troops trained when I get this fortress up to size 4, for the building bonus-ed traits added to the troops.  [Choose one of three = Always move first (which is not always true), +3move+3attack on first move (not as helpful if you have 'rush,') or +1hit points/per figure.]

Now, I have only tried a few soverings so far.  The beastlord seems like a really cool way to go, and early game, is quite powerful.  But the beasts (even experienced ones) just don't keep up with well trained and magic-ed troops.  Perhaps, if they were not restricted to solo figures, but could be combined into multi figure troops, like companies, etc., that might be different.  But they are single figure troops, and just not worth one of the nine slots in a stack, mid-late game.  Same for the death guy, who gets demons /elemental from the shards.  Early game they kick serious ... but by mid game are woefully outclassed by regular trained and equipped troops. 

Hope this helps you get a handle on part of the game...

Diplomacy

Understanding diplomacy can be difficult; how it works is not made very explicit.

The AI prefers to declare war on weak opponents and the weaker an opponent the more likely war will be declared. The strength of your army factors into the faction power rating which determines your power versus other factions. If enemy factions are looking like they might declare war, avoid going after that monster army or quest that might wipe out your army. The decrease in power rating may be the tipping point and the AI might declare war.

Offering tribute is a great way to avoid war... for awhile. It's not explicitly stated, but offering tribute does not allow either faction to declare war for 30 turns (and unlike trade and economic treaties, the AI cannot cancel these if relations worsen). If you initiate the offer you can save yourself some gilder as you won't have to offer any of it up front (unlike when the AI demands tribute of you). However, the AI will only accept tribute from you if he's Cool towards you or better. After relations get Unfriendly or worse, you'll have to hope for an AI initiated demand to postpone war and that demand comes with an upfront gilder cost.

Don't declare war unless you have a really good reason. Declaring war reduces relations with other factions (i.e. if you declare war on a Kingdom, other Kingdoms will dislike you more). You'll get attacked eventually, so be patient. In the meantime build up your army and cities, and when those first waves come, take advantage of those upgraded outposts that you placed on key avenues of approach. Once the first wave is dead, go on the offensive.

Seems to have worked here...

First victory via Spell of Making

World settings - Quest Dense, Monster Normal, Magic Normal, Resource Heavy, Slightly accelerated research and production.  Normal Difficulty.  Hey I'm a newbie, gimme a break.

Faction - Men, Lucky, Master Scout, Enchanters

Sovereign - General, Tactician, Life I, Attuned, Procipinee's Crown, Dragonfly Bracers

I got my first hero, an air hero and in an RP reason (Lady Lani was a jilted lover), stole his soul and gained Air I.  She would only use the spell once more as she regretted the hasty use the first time.

I started out with four cities, meeting most of my neighbors through scouts, but never made it past level 10.  The first city was a conclave, but I made the next one a fortress and the last two towns.  As the seasons went along I declared war on Resoln and barely lost one of my towns over to them (my main army was one-two spaces out of reach).  It was a pyrrhic victory on THEIR part as their main army was taken down to one unit (Ceresa herself was defeated).  She was killed less than three years later during the last stand of Hagudst, which became my second conclave city. 

The wars with Tarth and Ythril never amounted to much as they declared war, got scared and sued for peace.  Suited me just fine.  The war with Magmar, who declared war on me despite being the WEAKEST faction, ended up with him surrendering, and Lady Lari, the Sovereign using Steal Soul once again in symbolic execution of a hated foe.

I ended up defeating Vertar, the Frost Elemental King.  Bit of a hairy battle, but my sovereign was the last survivor, as I felt this was the best was to fully retire my long outdated Defenders.  From that I got the Heart of the Glacier, making my summoner into a warrior princess.  She never really made it that far as a summoner, only making it as far as Lightbringer.  She DID however gain Air IV to eventually have two transport spells (Call of the Titans and Cloudwalk).  

With fully upgraded flame staves and doom maul sargeants, both on warg cavalry, no army could touch them. 

It was only a matter of time until the Spell of Making was finished.

Help me!

Trying a custom faction

Decalon + Binding, Amarian blood. (Not sure if it's worth getting a weakness just for adepts for shard shine upgrading)

Strategy is simple, grab lots of shards using arcane monolith spell,  will automatically grant you elementals too via binding. Since you have a lot of shards, might as well get Amarian blood so your units and sovereign will gain initative, spell mastery, spell resistance or hitpoints depending on shards you own.

Having problems coming up with a good sovereign to complement this though. Any ideas? Thinking going with Summoners or warlock... 

Or is this whole idea lousy?

Idea good and interesting. Sovereign could be fire-air mage (i would grab fire later in game, at low lvls it wont help that much as air). Life for healing your minions would be handy either especialy if you get that healing ring and devouted perk.

As long you took decalon, you can grab air/fire in game via books or heroes.

For talents: general, briliant, tactician, clumsy and 10 perc exp +2 spell mastery per lvl. take staff for extra 25 perc. damage. Dont take warlock, general better in loong run.

In mid game fireball/flamedart everything. Use minions for keeping enemies away from your mage. you can pick lightbringer for tanking either its not so deep in tree.

I love playing magic-oriented games, I can't resist replying even though I'm a bit late...

Unfortunately, the 'mage' professions are not that great. "General" is the easiest (and most boring) profession to play, especially as a mage, since many spells have a 'damage per level' component.

If you have binding, it might be slightly better to play as Empire, because Life shards don't have an Elemental, while Death shards do. You can still play Amarians, if you like their magic-y feel. Their spell is worthless, though.

I suggest taking Life or Death magic, as you can't buy it later from the Decalon. A second magic school is optional. Take Brilliant and Procipinee's Crown, the rest as you see fit. The Staff of Souls looks cool, but it's almost impossible to get any benefit from it. Like others have said, Clumsy is a pretty harmless weakness.

If you like to do damage in combat, Flame Dart (fire) and Horrific Wail (Summoning Tree) are nice spells. Don't expect to do a lot of damage in the early game, though. Therefore, be prepared to often switch your role and smash your opponents in the face with your 'spellcaster'. Especially if you are lucky enough to find some good items.

Lastly: be agressive. The elementals from Binding are relatively weak. Use them well while you still have an advantage.