Depends -again-of how much scripting help we will have.
Authority of both Roman Emperor and Bulgarian Cral/Tzar will be based on how many "missions" given by the nobles counsil will be successfull! A wining king has more authority than a losong one.
Events will be the 2nd cause of rebelions.
Losses in cities by invading enemies will cause upprisings.
Finally happynes and law order are also factors for rebelions.
Normans will apear as a small raiding force easy to be defeated some time around 1000AD . That event will triger Normans as mercenaries for Lombards.
A full scale Norman invasion will take place a couple years later.. Please read again our Norman preview so greatly made by MATTHAEUS.
You will notice that Normans have "early" and "late" knights. Lombards and Roman used Normans as mercenaries but also Normans coppied the roman and lombard heavy cavalry shock harge plus adopted many "mediteranean" armor ellements.!
As i said ,everything depends of how much scripting help we will recieve.