Hey, sorry for the slow reply. As I feared, I have become very busy, and have almost no time to spend on this project at the moment.
1) Tribes are a first attempt at "Minor Factions". They were intended to be less complex than a full human society, but introduce an interesting new element to some parts of the map. For now, they don't do much at all, but your agents can cause them to attack the nearest human settlement if you can find a "tribal gathering point" settlement, and use its power.
2)Prestige is mostly earnt through activities. Host gains an amount determined by the cost of the activity, and everyone gains some based on the prestige of other guests (so it's valuable to be able to invite high-prestige nobles). You can then gain bonus prestige through a mask at an event, and one of the agents can affect noble prestige as well.
3)You can't change your city's production aims at the moment. I wanted it to be a way to force you to ally with certain others (those who share your industry) and oppose others.
If I get time, I want to definitely allow the player to build their own settlements. They'd own a city, but around it would have various dark buildings. This could include sea-based things, such as fishman cities.