Easy in Stardock games is usually not easy at all.  For me it helped a lot to get leather and spears quickly, without armor your troops are going down very quickly.   I also find that elite troops are much better choice rather than spamming crappy but cheap troops.  If you are rolling in money build more troops and go after the A.i asap because they are not going to stay peaceful.

Spamming cities should be high priority early game because the A.I will be doing the same and there almost isn't any downside having lots of cities. 

Cant comment on Magnar as I always play with custom sovereign

Take 4-5 civ techs first, then go all war techs for a while. Design units that are upgradable (chose the option with the green arrow beside it when you take weapons and armour). Make your first little army fight monsters all the time to level. When war comes use this army to go straight for his best army and take him out. Rinse and repeat. Or get the death demons (from death shards) of Ceresa and make them split by delivering killing blows. That makes the game very different and fun

Death shards are the same thing as life shards - depending on which side you're on (kingdom/empire) when you build over one of them, they will change "color" to match your faction.  Ceresa (Resolyn) also has a spell that can turn any type of shard into a death shard.

Yes champion injuries can be removed, by rare loot potions that you'll occasionally find from quests.  But if you get a heavily injured champ sometimes its better to just station them in one of your cities, both for added defense, but also stationed champs reduce unrest - so a stationed champ will increase your production and research in that city.  So no, I wouldn't destroy a champ ever.  Also if you have more than one champ in the same army stack there will be less exp per hero (it splits more).  So you'll level more slowly.  Usually I go for 1 champ per stack, but you can get +exp bonuses to everything in the army traits on level up (found randomly at later levels) , or things like "potential" (+exp at lower levels) so if you want to put several champs in the same army it won't cripple you.

That's about my same tax strategy.  I rarely touch taxes and just sell monster loot if I'm low on gold.

I'd agree with the above on Magnar.  I'd suggest with him building some slave units (they build really fast) and send 2-3 along with the lord as meat shields while you level up.  Plus some of the special spells that Magnar race gets to kill a unit to heal/ buff work well.  Building a few really cheap slaves to send out solo as expendable scouts (setting them to explore) works well too for the early game and lets you know where good places to settle might be.  Researching some civ techs to start is always good, up to trading. The blind spell as any of the empire factions (death spell) can be very powerful, especially against archers.  Magnar is generally magic themed, and fireball can wipe out armies nomatter how much armor they have - so if you can grab a rank in fire magic, try that out.

Hope it helps!

I also wouldn't worry about the Magic techs that give your units magic items unless you have crystal income. 

I'd also say when it comes to the Civilization techs Joasoze  mentions, Trading is one of the most important, opens up roads between cities.  Restoration is probably the #1 thing I'd research after civics.  If you can't build a logging camp, because not located near a forest, the workshop will most likely be your first production improver.  merchant is also good for added income.  means being able to buy/rush things or pay more wages. 

There's a short period of time where lone champions are good.  Soon you should give them some troops to travel with to take harder monsterrs.

Re: Death Shard Question, well they will power up spells under death magic. 

Re: Magnar.  This Sovereign has a strategy to employ unique to him/his faction.  First off, he's a warlock.  He'll do the most damage blowing up things (or burning them ) with spells.   He can train slaves and they cost no wages.  That's right.  No wages.  Train as many as you can as often as you can.  Use them as fodder.  There's even special spells that make them blow up and do more damage.  I would make a few good defensive units that weren't slaves and use slaves to fill out army stack.  Make border defence forces.  Prepare to take out your neighbor.  Burn baby burn.  Definitely want to get Magnar at least Fire 2 or Fire 3 on the levelups.

I was in the same boat as you until I understood that Easy mode can actually mean Medium to Difficult in some aspects.  I suggest you drop down on level (to Novice or Beginner-forget which) and set the distribution of food/materials/essence to dense.  This latter option will make it easier (but not too easy) to find good areas for new cities.

Once you get good at that level, move up one.

Yeah, it's a common misconception that "Easy" is easy.  While they may tout they've yet to crank up the pain for the advanced players.  But to a new player.  "Easy" can be a wake up call. I felt that way till I played more than several games. 

Also the slave scout is probably good idea so you could make them fast and send them out in all kinds of directions uncovering the map much more faster.. 

Good luck and have fun

A couple of things to make your life easier:

First, Magnar (the faction) isn't really a good choice to start out the game with... they have a mechanic (slavery) that requires a bit of planning and demands a certain play style to make full use. In general, it's better to make elite troops instead of cheap ones (due to army limits and stack of doom effect), Magnar turns this on its head with lots of cheap troops that just aren't very good unless you're using it in combination with very specific sacrifice strategies. I'd recommend trying a more traditional faction like Kraxis or Gilden until you are more familiar with the game.

Second, it's generally better to play on larger maps in the beginning (but don't fill it with too many players either). Bigger maps often gives you some room to expand and thus more time to experiment/get used to the game.

Third, money should be spent, it's not doing much good sitting around (unless you are using a very specific income strategy). In general, if you have spare money, buy stuff with it. Rushing key infrastructure in the beginning is particularly important because it has a much bigger return. I like rushing unrest buildings or gold production buildings as it pays back via more taxes that I can then used to rush other things. Just keep a bit of gold around for emergencies.

Fourth, don't put multiple champions in the same stack unless you absolutely need to (have to beat a certain army and need all you can muster to do it). The reason, as others explained, is due to reduced exp gain when you do. This means even your sovereign should be alone. Accompany your champions with troops, summons, or whatever else you can make without too much trouble (don't spend too much production turn making troops early). The main goal is to be able to beat monsters without losses and level as fast as you can, leveling is important, because without it, heroes are pretty weak.

And finally: Try not to get your champion/sovereign killed. Not only does champions gets injuries, they also are taken out of the game for several turns (that sets you back in your early game efforts). Experienced player do this instinctively by knowing what they can fight and avoiding those they know they can't win. For new players, don't be afraid to save and reload.

I can post stuff, but afraid it will lose context in all the other posted stuff.

Magnar is fine as a starting sovereign, that said Magnar is played differently than the other factions.

There are a lot of different tactics to embrace, first rule of elemental: You always need civilization technology, you cannot see the 3 tech tree's as separate, they are 1 big tech tree divided to confuse new players .
What I mean with this is you need all the different tech tree's to be competitive.

I recommend getting a few civ tech's (one or two) right off the bat, then get the technology to use spears and leather armour. When you can field leather armoured spearmen (you have to design them yourself). Field some units of these (a general tactic that works for each faction too).

To start off with, it can really help designing a unit with "Staff, Weak", build one of those units quickly to accompany your hero and act as meatshield.
As Magnar this tactic differs to "Slave, Staff". and you can build 2 or 3 to accompany your heroes. Also as magnar its easier to divide your two starting heroes into 2 stacks (that really boosts xp gained per turn used).
If you have 2 heroes in the same stack, you will divide all XP gained by 2.
If you have 3 heroes in the same stack, you will divide all XP gained by 3 (for the whole stack), and so forth,
so if you keep 1 hero with trained units they will gain full XP, and can go around killing wolves, mites and darklings until your heroes get to level 5.

Run with "No Taxes" until your initial city reaches level 2, this will boost tech and construction time in the first few turns while sacrificing 0.4 gold per turn.
Do note that cities with 2 grain will note level up to level 2 unless they gain a food bonus.

Also, start your games by aiming to expand, you always have to build new cities, especially right off the bat, the first unit built should always either be a lumber-mill or a pioneer, and then build a few more pioneers for good measure.
(Only build lumber-mill from the start if your city have 3 or 4 materials).

These are a few quick tips, hope they help, if you want more just ask.

Sincerely
~ Kongdej