I think "Arakanese" culture is fine. But it definitely should be Buddhist instead of Sunni.
There is no Arakanese culture in-game, and I don't think we really need to add one. Burmese is fine for both provinces and the state.
Thanks for the suggestion.
Arakans state religion will be changed to Buddhist and the province conversion will be removed as per the suggestion.
As for vassalage: It's my understanding that politically the closest ties Arakan had was with the Ganesa dynasty which is gone by 1444 (if still in fresh memory) and that it mostly extended to paying tribute. For much of this period Arakan is considered a rouge pirate haven by the Bengal Sultans (and the Mughals after them) and judging by that it seems they felt their control over the area was limited.
Speaking about paying tribute, most relation between nation in Southeast Asia is simply paying tribute without any vassalage (there are vassalage but the primary one is tributary), so can we expect somekind of mechanic developed to represent this in the future?
Might I inquire what your sources are? I'd love to read more about the region, but I have no idea where to start.