1. Maybe 15 delay would be enough for something like that. Or 30. It's a sort of axe, no? Did you mean +1 for the tepoztli?
2. By looking at them and reading the description. If the description is of no use, then go by the looks. If that still doesn't work, guess.
For the Expansion campaigns? I don't think anyone has put that much work into them. You can see the upgrades of each unit by correlating the numbers in EDU with the text in expanded.txt.
3. For cavalry, the mass in EDU does nothing. People usually leave it at 1.
It tells you what to do for units with no shield, using rustic weapons, and multi-layer armour.