Installation is fairly straight forward. Extract the files. You will get 3 more zipped folders labeled exactly what they'll do. They overwrite each other so you can extract one directly over another without having any wierd anomolies. Extract them to your data folder and you'll be ready to play.
This will completely replace a race of your choice with the cuotl, all cuotl abilities and units are unlocked except for the ones mentioned in the bugs.
The following bugs are known and to my knowledge, currently unfixable:
Building animaions are missing(can't have animations without animation files)
Sounds are missing(I'm guessing they only added in sounds for the vinci and the alin for this build)
Holy districts do not extend the borders of non cities(couldn't get this to work, its coded differently from the rest so the conversion is not possible)
You cannot make a statue by placing three temples near each other(that's what the code said is supposed to happen, I don't think its that important and it has the same conversion problem as the above bug)
Cities with military districts do not auto heal(same reason as the two previous bugs)
Making a truce with a neutral site costs energy rather than timonium(same reason as the previous three bugs)
Heroes do not level up properly(it uses the alin system for leveling which is researching ability upgrades. Since you only research ability upgrades twice wand that occurs when you upgrade a city, any level beyond two is unattainable, I have no idea how to fix this bug, I'm working on it but I don't think it is possible. I could attempt to counteract it by altering xp values but that would violate the purpose behind this mod which was to simply add the cuotl in and not change them in any way that could be imbalanced).
These bugs are present in any of the current modifications that introduce the cuotl. The two I know of actually have more bugs(for example, you can buy cities for free in the others).