fktifzobr
The mod for additional upgrades was originally an NCF mod made, I think, on Heroes community; the second upgrade for humans is probably the green upgrade from our forum
In theory, all of this should work even without other creatures
As for additional upgrades for the town, you need to dig into other mods; for example, it's done in Blade of Armageddon. Those are complex manipulations — you have to add new buildings, define their connection to other buildings, and specify them in the construction file and in the town on the map
There was another mod for additional upgrades on the forum, but I don't remember where it is or what it was called; their mechanics are simple — when a building with additional upgrades is constructed, they replace the basic upgrades in the recruitment window