I'm upgrading the city guard; now they will be at level four (in Dark Messiah, they are REALLY STRONG; if you summon a guard and a vampire using a code, the guard will win). The upgrades are Storm Guard and Black Guard.

Awesome! - I once suggested making a mod to replace one of the cities with a free city (let's call it... just "Free Cities") - in principle, many units from those cities are already ready, and most importantly, they are not invented but real (well, for Ashan, that is), meaning they are the ones that exist in the lore.
But in general, according to the lore, are there 7 types of units for such a city? - As far as I know, the Crimson Mages went there after the fall of the House of Chimera, plus various mercenaries (Wind Blades and Black Guard), as well as priests of Ilat, and... I don't know anyone else.
We could be simplistic - level 7 - air dragons.