As you already stated, the peaceful relation path leads to more events. So it might be an absurd idea but back in ck2 i often combined the events from sunset with the roman restoration mod ( the one with portal invasion) . I´m not saying this would fit in your scenario but given the fact that there are fewer events in a hostile approach towards the sunset invasion you could think about adding stuff that is already in the game but not used like the roman culture and hellenic faith as a counter towards it. i have no clear vision how that all could possibly fit in but maybe something like you meet someone with a strong cesarian family name somewhere and he asks you to give him a title and help him restore roman power so the mediterean world has an answer to the new threat without only falling to their knees. the roman culture is already fully implemented within the game but not selectable as a rulers starting culture and writing an event for that shouldn´t be much of a problem for you when i look at the events you already created so far.

There would also be the option to expand on that idea and (if currently possible for modders) add fascinations to those dead cultures like some benefits for your legions against nahuatl only, similar to the ones some holy sites give you. That way no AI could accidently research and use it without having the event fired before.
And looking at nahuatl culture right now i can´t see a difference to other cultures but maybe i miss something. It would be great to give the fascinations different names and if possible even different boni or unlocks so the player has an interest to bend the knee and adopt the culture at least in one playthrough.

I dont know how possible this would be but it would be cool to see other new world nations that were mentioned in ck2, I know there was an inca with guns, the iroquois confederation and some plains nation. Could be interesting to give the aztecs some competition with other nations that approach and treat the player in very different ways.

I'm not sure how possible it is considering the lack of an "offmap empire" system like jade dragon from CK2, but some interaction with them while still remaining an independant power would be nice. perhaps make it easier the stronger you are to both limit the AI's potential of doing stuff and to make it somewhat of a challege for players, but something like a trade system or other forms of peaceful interaction would be nice in the same vein as the Jade Serpent mod from ck2

Also, It would be nice for the added cloths/hats/whatever to show up in the barbershop, because it doesn't seem like they are there now

Just wanted to say here that I am reading and enjoying all these suggestions; I just don't have anything to say in response for the most part :) Will let everyone know if I end up implementing anything here more or less exactly as proposed. E.g. the Incas and Iroquois are some of the most common requests; so I will try to find a specific way to make them interesting and fit the lore.

So this is something that imo was lacking the most in CK2 Sunset Invasion, colonial cultures that develop and split off from the original invader culture.
Maybe you could create one colonial culture for every culture group?

@Kaiser Interesting... though unsure how to do those melting pots. Not very realistic to just have a Norse-Nahua culture with both the names Asbjorn and Quauhtlapochin; but transliterating one to the other is a toughie.

The Nahua culture would be the dominant one and so I would say that, in the example you have given, the Norse names are transliterated into Nahua-esque ones and maybe some title names change too

in vanilla we can have a dog or a cat or maybe even both if they don´t kill each other and that´s it.
maybe you could introduce some mexican animals like opossums, manatees, armadillos, sloths, anteaters, tamanduas, howler , spider monkeys, porcupines, agoutis, pacas, squirrels, chipmunks, beavers, gophers, prairie dogs, tapirs, kangaroo rats, voles, shrews, bats, and maybe even whales and dolphins for some more funny events when you own land near the ocean.

Just a proposed idea / a couple suggestions to fix the event troop issue - I noticed the "landing" modifier that gets added to counties significantly increasing levy rate for an invasion.

2 things:

1. If you conquer the specific landed county, you keep the landing modifier until it expires - this is very broken as it allows you to get the 10-30,000 levy bonus to yourself, or theoretically the AI to get it as well. A trigger-action that immediately deletes this modifier if the county holder is not an invading culture/religion would probably solve it quickly.

2. Since the AI doesn't use event troops, I'm not sure what the rational is behind them getting ~50,000 event troops once they form their empire title (i set them to a higher difficulty which may be why it was so high). I think a work around for the event troops is after winning the initial landing and forming their empire, instead of getting a bunch of 1-time-use event troops (just due to AI incompetence), they could get a similar levy increasing modifier to what exists, alongside maybe a control maxing modifier to the counties they specifically hold (to allow for instant large levy size), and if gold is an issue in raising them, adding a levy-upkeep price reduction to that modifier as well could solve that.

Just some ideas - in two separate 1066 games I've seen them swallow up Hispania and Iceland and then not really do much past that since they tend to declare a easy war with their "50,000" levies, but then promptly lose it when their ruler marches into battle with a 900 levy army and gets obliterated. Also worth noting that the second crusade will likely be for a Kingdom in Spain if they conquer it, and that gets rolled over by the crusaders since they don't actually have their full levy size / access to their event troops.

@Ryantdpla #1 is pretty much a bug in the mod; will have it fixed asap. #2 is... complicated. AI uses the event troops in most cases; I have seen them use their full doomstacks against a crusade against them, which they ended up winning by a hair. The issue you describe of them no longer using the doomstacks is erratic; I cannot accurately predict when they stop using the event troops.

What you say has crossed my mind before, but I want to make that a last resort. You may notice a disabled decision for the AI to request more event troops in exchange for gold. I want to hook it up to a system so it counts how many troops they have and when they want to activate the decision, to set different AI strategies for different difficulty levels - and different personalities for the conqueror.

That would be much harder to implement with those county modifiers; or it could, but with very messy scripting. I am going to wait and see for now, because in most of my testing games they do end up using event troops for a fair while, and maybe the devs will fix the event troops thing in 1.1 or maybe 1.2. Otherwise, yeah, I may have to resort to that.

Having more conqueror empires rather than 1 main empire imo seems more of a realistic scenario. Given their technology it would be extremely hard to keep centralized control over the atlantic under 1 state. Having conqueror empires could change things dramatically as they would fight each other for more land/glory as well as subjugating the rest of europe as well. Allowing you to align yourself to one or none at all.

Cultural melting pots from Aztec conquests would be an interesting parallel to reality, where Spanish conquest of the Americas led to new Creole/Mestizo dialects, customs, cultures, even delicacies. Some regions to try it in off the top of my head are in Iberia, Ireland, France, or Iceland.

In general, more events to show Aztec interaction with the European peoples in different parts of the world, be they subjects within their colony's borders, or near the borders.

One suggestion, or Idea for a submod, could be something akin to the jade serpant mod for CK2? I always personally loved the idea of the Aztec Empire acting as an offmap power like china in CK2.