Hard to say on Silesia since we don't have much data, I could see 2 of the provinces being German but 4 is too many and would reduce Silesian to one province, German settlement really sped up under Austrian and Prussian rule, ideally there would be missions for both and Germany to start settling Western Slav territory
Yeah the Kashubs are missing from Wolgast and the Teutonic Order, part of forming Prussia should be converting the non-Germans of the land, ideally would be expanded to Livonia against the Baltic people
Agreed, Azeri and Turkish should be in an Oghuz group, could add Gagauz and Turkmen though that's debatable
Luxembourgish would be nice but the developers are trying to avoid one province cultures, should at least be Rhenish
Arpitan probably should be added and would work for Romance speakers in Switzerland and the French Alps
Hungary should have a difficult time reigning in all the different cultures, they were and still are the odd man out in that region, they came from the Urals after all, and as much as it might annoy Romanians I would still keep them with Hungarian in the Carpathian group for simplicity's sake. Due to the hassle of adding the culture group swap decision, at least according to developers, I think the best solution would be having Slovak moved to West Slavic and giving Hungary a permanent modifier at start which grants an extra culture acceptance slot and is removed if Hungary removes Slovaks as an accepted group, this would represent how Slovaks had been integrated into the kingdom after centuries of Hungarian rule while still granting Hungary the ability to accept more cultures as they expand in the region, such as accepting Transylvanian, Croatian, Serbian, Bosnian, Romanian, etc. But if Hungary wanted to, for some reason, they could revoke the accepted status and the modifier would be removed.
The Safavid dynasty came from Ardabil but they were not Azeri, they were Kurds and themselves came under heavy Turkish influence. A Turkic (or whatever you want to call it) culture group would work, the Ottomans should have a hard time keeping all the different cultures of the empire as they grow bigger, by running out of acceptance slots, embracing humanism or converting the ethnic and religious minorities, at the least they need to be removed from Levantine and they cannot be put into Iranian for obvious reasons