It is very nice thread, I have to give you the credit.
And I do not want to spoil it, but I have to state, again, that I am really against this upcoming dlc and starting date. By my opinion it should start at earliest on 1054 and finished as it is now 1453 (full 400 years) with focus on Christian (and eventualy muslim) nobility and there interactions and wars. This is very nice thematic for different kind of game (maybe a game for mechanic and period from 700 to 1100).
Aside from that, here are few things to add to your thread.
Serbs (especially those who adopted orthodox Christianity) still use (celebrate) many things from pagan period that are shown on your picks. Someone already mentioned “slava” that you have in post above where you have a “lunch” (trpeza) with candles. Custom in the spring with flower coronets (usually on the. St.Georges day) and most important burning the trees or branches that is still in use on a Christmass day eve, either in front of churches or in homes. And everybody gather around. And the more sparkle the burning tree made it means more joy and happiness in that year. It is all a bit modified as Danubian Cossack said.
And actually the main reason why majority of serbs accepted east over west Christianity (and they could both since they where located where this two meet) was that east one was more flexible and west more rigid and Byzantine missionaries let people leave there own pagan custom and incorporate them into new adopted religion, opposite of westerners who where more strict. So it did stay until nowadays.
About separation (or uniqueness) of south Slavic tribes. My opinion is that it should be just two (croats and serbs) and Bulgarian if you speaking of slavinized Bulgars. As the rest were more tribes of the same “nation” . Byzantines called Serbs by that name but also were known as Triballs (spel?) because of the fact that whole population was made of many smaller tribes united under one name.
And one more thing (question). Some of these Slavic people where in two places at the same time. Like Wends that you have it in west group but starching all the way to south. Or Serbs who partially came to Balkan peninsula and partly stayed in what is today east Germany. I know that they are two different nations today (one almost completely distinguish (and the other on the good way on the same path
)), and thay are called different Sorbs, and Serbs, but they were the same at the time (and they still call themselves the same “Srbi”. Do you think that should be represented or not?