What’s the special red resource required to forge the Shard of Icarael

• By default, you'll heal a very slow 5% per turn.
• Standing on a friendly city boosts this to 10% (garrisoning has the same effect; it doesn't stack).
• Watchtowers give you 20%, and this rises as you improve them to Lookout Towers and Remotuscope Factories

This may not be enough, though, so you can also:

• Ally yourself with the Sisters of Mercy. Each of their villages gives +5% per turn, which can add up to a huge bonus (healing 1/3 of your hp per turn with 5 or 6 such villages).
• Get a hero (necrophages or sisters of mercy) with a skill that boosts % healing per turn).
• Win the Legendary Deed that gives you Intelligence Corps for a flat +20% per turn.
• Build the Medical Center and/or Inoculation Station buildings in your city (for roughly 25% total).

These would all add up to a ton of regen; really the idea is that 5% is slow enough to really cramp strategic movements, because it's a painfully long 20-turn process to heal your troops if they get badly hurt - but by the time you're up to 25% or so, troops can fully heal in a mere 3-4 turns.

So the purpose of having all these different ways to heal your troops is that they cover each other if one of them becomes unavailable - if you can't (or strategically don't want to) get the necrophage hero, you can grab a different source of regen to get by. If the enemy grabs all the sisters-of-mercy villages, you can invest in the technologies - if you have the sisters, you can completely skip those techs/buildings and get ahead other ways.

You could stack everything for a wacky 60-70% regen per turn, but it's really not much better than 25% - by the time you reach 25% or so, you're healing in a few turns, and your meaningful military power is less about weathering repeated assaults, as it is about your units not getting killed during an individual assault - as the old saying goes, you can't heal being dead.

This is also because usually you're only up against a few armies; you're not withstanding some constant onslaught - if you survive to heal at all, you've almost always killed many/all of the enemy fighters in their army, and usually they only have a few armies in any given war (and will sue for peace after those die).

Ok so I found some answers on Amplitude forums.

Battlefield and positioning

Yes, you have to engage your opponent on the tile side where you want to locate your army. If you hover your opponent while you keep right click pressed, a preview of the battlefield will appear.
Reinforcements are simply the other armies that are located in the battlefield.

Turns

In a nutshell, it's not implemented yet:

In the final game we plan to offer a game setting that will allow you to control every round if you wish so. It will probably be 3 settings: simple (1 order phase), normal (3 phases), advanced (6 phases). In all these setting we always keep the same number of rounds (6 rounds), not to change the game balance.

Ranged attacks

Same as for turns: it's still a work in progress.