Ref: Dol Guldur
Don't know about the file types though it is confirmed that BI will use a different file type for save games, though I cannot locate the reference right now.

Concerning Culture groups, if you read my earlier post to you a little more carefully you will find that there are posibly 5 distinct cultures as in Vanilla.

Firstly there are the roman factions now shrunk down to one: The Western Roman Empire.

Secondly the Greek factions now represented by the Eastern Roman Empire.
Ref:"the rich part of the Roman World, and now reverting to a more ‘Greek’ and Eastern outlook than strictly Roman. Their heavy cavalry is frightening indeed."

Thirdly the Eastern factions represented by the Sassanid Empire.

Fourthly the infantry based barbarian factions such as the Franks and the Saxons.

Fifthly the nomadic barabrian cultures such as the Huns and the Sarmatians.

Hope this helped.