I´m thinking keeping the slow and durable in the middle, they hold while the flanks deal with their own enemies, in order to swing inward and deal with the rest of the middle. I´d like most of our artillery to be focused in the middle, in order to better support the flanks. I also want us to big on units, with 10k it will quickly get swamped if we field 10 untis of outriders and 5-strong knights, instead almost all cav should be in 20+ units and melee infantry 50 strong, at least.
As for shooting, I´m not sure how well Empire handgunners will be able to deal with Chaos infantry, also I think it will be hard to line shots with cannons. That´s why I want mortars, they don´t need line of sight, so even behind our infantry they can do some good.
On magic, I think we should get many lores, and try to get a mix of long-range lores and buffs, we want Chaos to come to us, at least in the middle. My suggestion is a Coven of Light for Banishment, Balthasar Gelt for Metal, horse-riding Beast Wizards with the cavalry, a Lvl 4 Heavens for the Comet, a lvl 4 Life to keep our big infantry alive and a few low-level Fire and Shadow for a mix of chaff-clearing, buffing and damage. With 3 flanks with their own magic, we can afford several lvl 4s.
A strong flank with units of 20+ knights, DGs, Stanks, Riding Warrior Priests, Captasus and Beast-Wizards
A durable middle with 50+ strong units of halberdiers and Greatswords, backed up by handgunner and artillery and a Life-wizard
A lighter flank with cavallry, some infantry and fire+shadow wizards, weakened to give the other flanks an advantage in points.