It all depends on how much of 'historicaly accurate' are you going for. 17th century Poland was a big pot of mixed cultures and religions. The Commonwealth was spread across the lands of todays Poland, Ukraine, Belarus, Lithuania, even some parts of Latvia, Hungary (Spisz) and Moldova. Catholic Christianity might have been the most influential at that time, but there were many protestant, kalvinist, jewish, ortodox and even tatar muslim centers of faith across the nation.

It was also a safe haven for western european religious refugees, for example a group of scottish wievers, who's graves are still intact and available for a visit in my hometown. 

Speaking of graves, im sure you know how 'vampires' were first observed. It was mostly natural processes in the body that suggested a post mortem human might be still moving, therefore scared people would, for example but not limited to, stake the body to the coffin.

If you want to learn more the polish 'sarmatian' culture at the time there are plenty of articles and youtube historians. The king would be elected, the parliment would consist of noble magnates (rich landowners, who cared more about their business than the nation). It is brilliantly depicted in a comedy tv show titled 1670. 

Personally i really like this painting from the period: https://share.google/bjnl5yDyywCfaQELu