Here's a synergized spread. We need the magic academy to get enough T2-capable spellcasters to include Arrow Ward in our formations, giving us some well-rounded and difficult to remove mixed units. Pike & Shot formations with arrow protection spells would be great.
I am a little worried that T1 pikes won't have enough training to pull off a pike square, but even T2 should give us enough to counter-position against enemy cavalry, or have sturdy bulwarks in our lines, while T1 static pike lines would stop their knights from knighting us too badly.
I'm not certain on pure human pikeneers. Pure orc gives us the best discipline. Mixed might hurt discipline in the short term, since we don't have much experience with combined forces and have an influx of humans unused to fighting alongside orcs. I imagine pure humans having better discipline than mixed, but with potential morale problems, since we'd be relying heavily on freshly conquered people. More numbers from the new conquests, and the morale problems shouldn't be terrible, so long as our coin is good.
I have little real preference for crossbows over bows, but crossbows fit our artifice theme better. I know the auxilia shoot already, but I want better anti-armor archers than our auxilia, and archers disciplined enough to fight in a pike & shot formation.
I don't like that we'd only be able to get light cavalry this turn from revising auxilia, but I don't see a better alternative.
I'm not sold on this champion's gimmick, or if it's even allowed, but it fits, and I think an offensive/duelist class would be the most useful.
Free Infrastrucutre: Magic Academy
Our mages are limited in numbers, and are little more than hedge mages with patchwork educations. We need to invest in a training academy to remedy this. As teaching dark magic can be dangerous, it might be wisest to build it in the nearby town of Hemlock Bastion Arnhold's Fall. Naturally, the academy will focus on training battle-mages, and teach military discipline to its students.
Artifice: Pikewall (T1)
We'll be fighting cavalry, and pikes are the answer. To ensure maximum pikes, both humans and orcs will be recruited for Pikewall formations. They will be given pikes, helmets, simpler mail, and a short sword for when battlefield conditions don't allow pike use. Their training will primarily focus on a static pike wall formation, where they stand in a line a few deep and point their pikes at the enemy. They will be drilled to stand firm against charging enemies while being shot at. They will only receive light swordsmanship training, enough to keep them from stabbing themselves.
Artifice: Pikeneers (T2)
The Deeping Guard are effective, but are too few to hold the line in a major battle. Pikeneers will recruit from humans, our loyalists mixed into forces recruited from our newly conquered lands. They will be given pikes, lightweight yet full armor, and short swords. While Pikeneers will be trained to form a pike wall and resist a charge, they will also be heavily drilled to maneuver in close formations. A square of Pikeneers will be expected to be able to fluidly move in any direction with pikes extended, and rapidly redeploy their pikes in any direction, or all sides at once. They will also receive slightly more sword training than Pikewalls, enough to out-duel militia or beat out-numbered footmen.
Artifice: Crossbows (T1)
We need a dedicated ranged unit to compliment our melee line. Heavy crossbows are an effective solution to Iserria's heavy armor. Lightly armored, these mixed racial formations will need to be trained in accuracy and formation movement drills.
Magic:
Arrow Ward (T2)
We need a one-way barrier that a mage can project in front of a formation of troops, to protect it from arrows while allowing those inside to fire back. After a brainstorming session, it was determined that we unfortunately can't easily solve this problem with fire or darkfire. Instead, a tall, arc-shaped zone will alter the velocity of physical objects in it, pushing them away from the caster. Enemy arrows will be slowed until they are practically harmless, and our own will receive a minor speed boost.
At this power, larger objects, like a charging horseman or giant rocks, will only see negligible impact. Arrows from the sides won't be slowed, but might have their aim thrown off, if the mage casts the arc wide enough to catch them.
Shape: Duke of Despair (Champion, Duke of Arnhold bonus)
We shall imbue the duke with darkness. The light imbued him after he was determined to sacrifice himself to save his daughter. ("A burning determination to slay a hated foe, at any cost? We can use this.") After we corrupt him, he will be filled with the =need= to destroy a specific foe, chosen once per battle, but not to the point he becomes a single-minded berserker. He will be more effective against the chosen target, but less so against others.
His shape will be corrupted. He will look almost human, but wrong. His powerful arms will be too long, his fingers ending in viscious poisoned claws. His visage will be a mockery of its former self, with horns and large jaws able to bite through metal. His size will be slightly increased, until he can barely fit into his corrupted runic armor. His flesh will be reforged to be more durable, and he will be given a slow regeneration factor -- Even should he fall in battle, so long as we can reclaim his body, he will eventually recover and return to fight the light once more.
He will be an offensive/duelist spec, filling a much-needed gap in our arsenal.
Edit: Pikewall(T1) and Pikeneers(T2) split off into two discrete unit types. The T1 variant is mixed human/orc for maximum quantity, and isn't trained well enough to maneuver. The T2 variant is pure human, slightly better armored, and is well-drilled enough to maneuver in square formations able to deploy pikes in any, or all, directions.
I prefer the Pikeneers, which will be more versatile for future battles, and not tie up too much manpower with people who can only stand in line on an open field.