Dancing Hoskuld
Deity
This is a good point. Well lets see, what makes a unit? I would say weaponry and training. But then what makes those? Weaponry takes technology, resources and manufacturing. While training requires tradition, insight and practice. Based on these we could have a set of requirements for each unit.
Technology - This would be based upon both the technology on how to make the weapon but the skills needed to fight in battle. Thus more than one tech could be needed.
Resources - These would mainly be the resources needed to create the weapon. Be it metals, sulfur, horses, elephants, etc.
Building - This would be used for either manufacturing the weapon or training with the weapon. Thus more than one building could be required.
Civic - Some units would be civic specific such as the Inquisitor.
Empire - Some would be unique to a specific empire.
So based on these we could get a better picture of how to plan things out.
I am not so sure about the training bit as I see that as an added feature to getting troops. Something we assume nowadays but even now is not always the case beyond showing which is the dangerous end of the weapon that is. Even basic training has changed over time, dance (also called drill) was a biggie in those times cultures and places where formation was important. AAArgh, I keep loosing connection and what I am posting. I will leave this for later.