PreScriptum: I know the suggestion forum exists, but this is just so large and detailed (almost a 100 new provinces and over 7000 words !) that I have to post it in a separate post. Sorry ! :)
I just realised I have to split my post as I can't post it as one thread...

I read that you would be doing a Balkan update and since I love your mod I wanted to help you in the small way I can- since this is my home region and I am quite interested in it's history.
The Balkans are a very complex region, with many polities and provinces changing hands, however, it is quite poor, so the level of detail necessary to represent it fully isn't possible even in a mod such as Beyond Typus. I don't expect all provinces I will list here to be included, and my proposals are mostly based on Wikipedia and Schoolbooks, so you can probably find better sources, and I certainly don't profess to be an expert on some of the areas-I'm sure my Bulgaria could be better and with the exception of Fagaras I didn't even touch Transylvania, but I hope this would be helpful to the mod team. I've read that you eventually plan to double( or triple or more) all development and rebalance the costs, to better make difference between 1/1/1 small islands or Siberian wastelands, and 1/1/1 province in Anatolia or Europe, so keep in mind all these provinces when you want to represent Balkans even better. Keep in mind that I'm Serbian so despite my best efforts I am (slightly) biased in Serb favour. That, and many other things such as inaccuracies and propaganda on Wikipedia is why in many cases I offer different options on province culture, to let you decide which way you will go. Also, my drawing could be better.
So, onwards to the provinces:
Part I: Slovenia, Croatia, Serbia, Bosnia, Montenegro, Hungary, Banat
Part I map: https://imgur.com/a/01f1T ALTERNATE: https://ibb.co/f55CVx
1. Pola/Istria: The Istrian province controlled by Venice for most of the timeline (ruled by Austria 1797-1806 and after 1813, Italy 1806-1809, France 1809-1813). It should be relatively rich, Catholic and culture could be either Venetian or a new Dalmatian * culture. Capital is Pola
* Dalmatian is a new culture on the eastern shores of Adriatic, representing higher class Italians mixing with local mostly Croat and in some cases Serb population. It's primary nation should be the new releasable Dalmatia tag. It would be nice to have events to switch coastal South Slavic cultures to Dalmatian when ruled by an Latin culture group nation, and to switch them back to Serbian or Croatian (or in Trieste, Slovene) when held by nations of that primary culture. It should be in South Slavic culture group, but you could make a case for putting it in Latin/Italian
2. Pazin/Istria
This province represents the part of Istria ruled by Austria for almost the entire timeline ( ruled by France during Illyrian Provinces 1809-1813). Catholic religion and Dalmatian culture (Croatian if you don't want to create a new culture). It should be much poorer than Pola, and maybe have hilly terrain. Capital is Mitterburg (Pazin).
Add a new Istria tag with cores on Pola, Pazin and Fiume (which I forgot to give a number, and should have it's culture changed to dalmatian), with Dalmatian culture
https://en.wikipedia.org/wiki/Istria
https://en.wikipedia.org/wiki/Pula
https://en.wikipedia.org/wiki/Pazin
https://en.wikipedia.org/wiki/Illyrian_Provinces
Maps showing the Istria divide:
http://www.zum.de/whkmla/histatlas/balkans/illyrianprovtext.gif
https://i.pinimg.com/originals/40/0f/a1/400fa173668de104cd5e7f643e181df0.png
https://i.pinimg.com/736x/32/8a/32/328a32e3d817867c2af243ef7c9bbcb0--republic-of-venice-maps-history.jpg
http://1.bp.blogspot.com/-xB4sha5y6UA/U3P7rYXUPuI/AAAAAAAAAEY/JZVTazb9CqI/s1600/Tabula_Ducatus_Carnioliae,_Vindorum_Marchiae_et_Histriae.jpg
3. Trieste
Same province, could have Dalmatian instead of Venetian culture to represent Slovene/Italian mix. Add the Trieste tag as releasable. Ruled by Austria for almost the entire timeline (ruled by Venice 1508-1509, France 1809-1813)
https://en.wikipedia.org/wiki/Imperial_Free_City_of_Trieste
4. Slovenian Littoral/Inner Carniola
An union of the above regions, representing the areas of Slovenia ruled by Italy between the World Wars, useful for roleplaying Italy. Also useful since it could be given to Gorizia before 1500, giving them more presence in the area and better representing their power. Capital is Postojna, and province name could be Kustenland or Innerkrain. Catholic religion and Slovene culture. Ruled by Austria for the rest of the timeline (ruled by France during Illyrian Provinces 1809-1813)
https://en.wikipedia.org/wiki/Inner_Carniola
https://en.wikipedia.org/wiki/Slovene_Littoral
https://en.wikipedia.org/wiki/Postojna
5. Oberkrain
Same province, capital Laibach/Ljubljana. Ruled by Austria for almost the entire timeline (ruled by France during Illyrian Provinces 1809-1813)
https://en.wikipedia.org/wiki/Upper_Carniola
6.Unterkrain
To break up the large and rich Krain, capital is Rudolfswerth(Novo Mesto). Catholic and Slovene. Ruled by Austria for almost the entire timeline (ruled by France during Illyrian Provinces 1809-1813). Could perhaps be owned by Cilli before 1458
https://en.wikipedia.org/wiki/Lower_Carniola
https://en.wikipedia.org/wiki/Novo_Mesto
7. Marburg, Cilli
Marburg is the old province, I realised too late I didn't create the province of Cilli for the Lords od Cilli. Ruled by the Cilli/Celje tag as Hungarian vassals before 1458. Both provinces are Slovene and Catholic. Ruled by Austria for the rest of the timeline.
8. Murakoz/Murvidek
One of the provinces I'm least sure about, representing today's Medjimurje and Prekmurje regions of Croatia and Slovenia. Ruled by Cilli before 1458, by Hungary after, and by Austria after 1527. Catholic, culture could be Slovene or Hungarian. Capital is Csaktornya(Cakovec).
https://en.wikipedia.org/wiki/Me%C4%91imurje_County
https://en.wikipedia.org/wiki/Prekmurje
https://en.wikipedia.org/wiki/%C4%8Cakovec
Cilli should get a Burgundy like event transfering their Styrian lands to Austria and Croatian lands and Murakoz to Hungary, and removing their cores everywhere. The tag's primary culture should be Slovene (the primary tag of Slovene is still Carniola), but rulers should have a German culture (expect Katarina Brankovic 1456-1458, who should be Serbian and Orthodox)
Cilli lands: https://upload.wikimedia.org/wikipedia/commons/4/41/Celjski_grofje_ozemlje.PNG
In addition to their owned provinces, they should have cores on Unterkrain, Oberkrain and Zagorje representing their lands there
9. Varazdin
Same province, owned by Cilli before 1458 to represent their Croatian holdings.
https://en.wikipedia.org/wiki/Vara%C5%BEdin_County
https://en.wikipedia.org/wiki/Vara%C5%BEdin
10. Zagorje
Same province
https://en.wikipedia.org/wiki/Zagreb
https://en.wikipedia.org/wiki/Hrvatsko_Zagorje
11. Modrus
Same province. Belongs to Military Frontier in later dates. Capital is Ogulin, and Karlovac after 1579. Should also have Serbian culture in later dates(and Orthodox religion).
https://en.wikipedia.org/wiki/Karlovac
https://en.wikipedia.org/wiki/Karlovac_County
https://en.wikipedia.org/wiki/Military_Frontier I don't know how to represent it the best. It had significant autonomy: freedom of religion, no taxes, etc... So at the least a province modifier or perhaps a Serbian culture march of Austria in later dates ?
12. Krizevci/Belovar
Represents the county of the same name. Capital can be either of those cities, or Korivnica, which was actualy the largest at the time, but Krizevci were a seat of an important event (The Bloody Sabor), and Bjelovar was certainly the capital near the end of timeline. Catholic and Croatian. Belongs to Military Frontier in later dates. Could also have Serbian culture(and Orthodox religion) in later dates, but less need for it than other MF provinces.
https://en.wikipedia.org/wiki/Kri%C5%BEevci,_Croatia
https://en.wikipedia.org/wiki/Bjelovar
https://en.wikipedia.org/wiki/Bjelovar-Kri%C5%BEevci_County
https://en.wikipedia.org/wiki/Koprivnica
https://commons.wikimedia.org/wiki/File:KoH-CS-Belovar-Koros.svg also a good overview of the counties
13. Sisak
The old capital of Croatia deserves it's own province, especially since it was important during the timeline too.Catholic and Croatian. Capital is obviously Sisak. Belongs to Military Frontier in later dates. Could also have Serbian culture(and Orthodox religion) in later dates.
https://en.wikipedia.org/wiki/Sisak
https://en.wikipedia.org/wiki/Sisak-Moslavina_County
14. Lika
Same province. Capital should be Gospic after 1604. Belongs to Military Frontier in later dates. Should also have Serbian culture in later dates(and Orthodox religion).
https://en.wikipedia.org/wiki/Lika
https://en.wikipedia.org/wiki/Senj
https://en.wikipedia.org/wiki/Gospi%C4%87
15. Krk/Veglia
I wanted at least one province for Croatian islands, and Veglia was by far the best choice. It was ruled independantly by the Frankopan (Frangipani) family until 1480, when it fell to Venice. The province and the new tag should have Dalmatian culture and Catholic religion. Pag was also the last place real-life Dalmatian culture(which was less prevalent than the definition I propose) was preserved in late 19th century. Capital is Krk. Owned by France 1806-1813 and Austria 1797-1806 and after 1813.
https://en.wikipedia.org/wiki/Pag_(island)
https://en.wikipedia.org/wiki/Pag_(town)
https://en.wikipedia.org/wiki/Frankopan
16. Zadar
Same province. Dalmatian and Catholic.
https://en.wikipedia.org/wiki/Zadar
17. Bribir
Named after the old Subic county. Capital could be Sibenik or Skradin. Added to further isolate Zadar and Split while owned by the Ottomans 1522-1683. Dalmatian and Catholic. Religion may change to orthodox in later start dates, but less likely then other such provinces(to represent Serbs moving to the Dalmatian coast)
https://en.wikipedia.org/wiki/Bribir,_%C5%A0ibenik-Knin_County
https://en.wikipedia.org/wiki/%C5%A0ubi%C4%87
https://en.wikipedia.org/wiki/Skradin
https://en.wikipedia.org/wiki/%C5%A0ibenik
18. Knin
Inland Dalmatian province. Capital is Knin,Catholic and Croatian(not Dalmatian, no Venetian infulence). Owned by Hungary/Croatia in 1444, to Ottomans in 1522 and to Venice in 1688. Austrian 1797-1809 and after 1813, French 1809-1813. Should be Orthodox and Serbian in later dates(Serb Krajina).
https://en.wikipedia.org/wiki/Knin
19. Split
Same province.Dalmatian and Catholic.
20. Neretva
Southern Dalmatia, owned by Hum/Saint Sava in 1444. Venetian in 1452, to Ottomans in 1499 and to Venice in 1695. Austrian 1797-1809 and after 1813, French 1809-1813. Capital is Mokro (Makarska), and Klis during Ottomans. Serbian culture (part of lands settled by Serbs, part of Pagania state, not yet influenced by Venice), could also be Croatian but less likely and Catholic/Orthodox religion. Culture changed to Dalmatian after Venice takes it, and religion to Catholic if it wasn't before.
https://en.wikipedia.org/wiki/Fortress_of_Klis21.
https://en.wikipedia.org/wiki/Makarska
https://en.wikipedia.org/wiki/Narentines

Provinces 16-20 are Cores of Dalmatia. ~1800 all Catholic Dalmatian provinces change culture to Croatian(other than Krk/Veglia)
https://en.wikipedia.org/wiki/Dalmatia
https://en.wikipedia.org/wiki/Uskoks - just a cool local unit

21. Ston/Peljesac
Second province for Ragusa, capital Ston, Serbian culture (bought from Serbia in 1321), religion Catholic(formerly Orthodox, but probably converted at that point). Culture would remain Serbian until later centuries, when Catholicism slowly assimilated them into Croatians (sometimes as late as 20th century)
https://en.wikipedia.org/wiki/Pelje%C5%A1ac
https://en.wikipedia.org/wiki/Ston
https://en.wikipedia.org/wiki/Serb-Catholic_movement_in_Dubrovnik - the SerboCroatian version of the article is written from a Croat perspective, but is very informative about Serbs in the Republic of Ragusa, so a nice read if a team member speaks the language. The gist is, the city itself was more Croatian in character, with a few Serb noble families, while the hinterlands were settled by Serbs and only assimilated much later
22. Ragusa
Same province. Dalmatian and Catholic. Ragusa tag should also have Dalmatian culture.
https://en.wikipedia.org/wiki/Republic_of_Ragusa
https://en.wikipedia.org/wiki/Dubrovnik
Between 22, 52 and 53 I later created the province of Konavle for Hum/Saint Sava,parts of which were bough local Serb rulers in 1433 by Ragusa, should have Serbian culture and Orthodox religion.Ragusan cores representing thir purchase of Cavtat,Capital is Novi(Herceg_Novi). Owned by Ottomans 1482-1687, and Venice 1687-1797, Austria 1797-1809 and after 1813, France 1809-1813. This province is not that important and it is small, but it makes Hum stronger, gives them another port, and makes sure Ragusa doesn't border Venice before 1699
https://en.wikipedia.org/wiki/Cavtat
https://en.wikipedia.org/wiki/Konavle
https://en.wikipedia.org/wiki/Herceg_Novi

23.Pozega
Same province. Belongs to Military Frontier in later dates.
24. Osijek/Veroce
Same province.
Pozega, Veroce and perhaps Valko and baranya should be cores of a new revolter tag, Slavonia
https://en.wikipedia.org/wiki/Slavonia
continued in comments