what about Braavos just using the valyrian model? i.e. we appoint a governor for you until you’re wealthy/organized enough to incorporate and run your own affairs

I think this misunderstands the purpose of Braavos’ colonies – given that the city itself is 100% urbanized and on top of a lagoon, the city needs its colonies in order to provide basic things like food, wood, etc. and it’s never not going to need them. So why would it ever want its colonies to be independent?