How does California work?

So I just recently restarted CK3 and started playing this mod for the first time. Began in California and am a little intimidated by the systems and government as it seems totally different than anything I’ve seen in CK3 before. I’m especially confused with what eurekan bureaucracy is? What the lieutenancy system involves? Why there are tax collectors? Why are taxes so low on vassal contracts? What does being the governator mean(in the mod, duh)? And why there are so many new options on the vassal contracts?

I’m also wondering how I should be playing as a ruler? Should I be aiming to get more or less permits? Should I be trying to reduce the amount of permits for my vassals? I read somewhere that the lieutenants will gang up under certain circumstances, but I haven’t seen this yet - when does that occur and what will they try to achieve?

Also also, I had a situation where an apocalyptic plague hit the state, and suddenly like 5 (peasant?) rebellions against the emperor started asking me if I wanted in on it - is that a new mechanic too?