You are a godsend, man.

Idk how skilled you are at designing events and such yourself, but if you are, it would make sense for ERE to start as a special subject type that Ottomans cannot just randomly break tributary status with at will, rather instead only a particular event chain around the release of Orhan would nullify the arrangement.

I remember trying to play ERE in BT before, I paid the tribute to stay as a tributary state, and they still dropped me anyway for no reason. Granada starting as a Castilian tributary should be a similar case where they cannot be dropped until after an event chain when the civil war ends.

General changes I would recommend:
1. All nations should be able to have tributary states. Limiting it just to China and Asiatic nations makes no sense.
2. All nations should be able to sack provinces at will, burning them down to 1/1/1 development and 100% Devastation from whatever they were before, for a cost of approximately 50 MIL points (same as bombarding a fort to make it not abuseable).

As a long-term suggestion, I would love to see a compatibility patch made between this and Europa Expanded, but modding that many mission trees to work alongside this would be no easy task.

Astragon I don't think he can do that, Beyond Typus is mostly a province/mission addon right?

What about adding or changing some provinces that could be useful for earlier start dates, if there is a need for it

i suggest transforming desert into provinces

diplomatic annexation cost should be halved or at least reduced in my opinion. development is basically worth half as much so subjects will have a much higher cost to integrate compared to how much power the land actually gives.