Concept for the forces of Robo the Necromancer.
Robo is obviously the C-in-C, but for now will remain out of the picture. Or off the battlefield, at least. That will leave various subordinates commanding in the field. I'm going to use the structure of Hail Caesar/Warmaster as a starting point, so armies will have several commanders, each in charge of their "brigade." So to begin with, I will define several subcommander archetypes, which will mostly determine the composition of their forces, but maybe to a certain extent will also determine their leadership capabilities as well. I think most of these will be unique, except there will be multiple Milittary Animators. Possibly more than one Spiritual Enslaver.
1. Military Animator: Animates undead troops, which are directly controlled by the leader, in a militaristic style. These will form the backbone (haha) of Robo's forces, and will be composed of typical skeleton infantry & cavalry.
2. Spiritual Enslaver: A manipulative leader, controlling the semi-undead & magically bound slave troops I mentioned before. Infantry & Cavalry of formerly independent humans, and possibly other races.
3. Agent Provocateur: Scheming necromancer who destabilizes towns/cities, then animates the dead into mobs of zombies. Since the Agent is more a social manipulator than military leader, this explains why the zombies are masses of sloppy, meaty dead compared to the more reliable skeletal troops of the Military Animators.
4. Vermin Lord: Allies. I have some Skaven and other rat themed figures. I like them, want to use them, and think vermin fit well with the undead. This is not a GW Vermin Lord, but I do like the name.
Other hazy concepts under consideration: Etherialist, Beastmaster, Constructor, Besieger. Maybe those last two are combined into an Engineer.
Also under consideration are individual mercenary or slave units that may show up in any of the commands above, as individuals, or maybe together in a sort of "evil dogs of war" type mercenary brigade. This is entirely based on either figures I already have, or things I may want to get & paint up for whatever reason. So far this would include (from my existing collection) Greater & Lesser Goblins, Myconids, and maybe Greater & Lesser Troglodytes.
Concept for Marienburg forces
Well this one is easier, as it's just a slightly modified version of the canon Marienburg, though my AltHammer setting will be somewhat different than the official Warhammer setting. So it will be an independent city state with a mixed relationship with the neighboring Empire. Since it's mercenary based, I will have less distinct brigades. Most will be mixed. I will keep the diverse racial composition. But I do have a couple of distinct brigades.
1. Mercenary. The core of the army, diverse troop types.
2. City Militia. Only present in armies directly defending the city and immediate environs.
3. Wood Elf Allies. I have a small 3rd ed. Wood Elf army. May as well use it on occasion.