What kind of siege weapons will be available, and to what factions?
Before we even start, cannons are not in whatsoever, I believe (duh)...
Reading:
Wikipedia
http://en.wikipedia.org/wiki/Siege_o...6%29#The_Siege
http://en.wikipedia.org/wiki/Onager_%28siege_weapon%29
http://en.wikipedia.org/wiki/Ballista#The_Middle_Ages
http://en.wikipedia.org/wiki/Trebuchet#History
It seems like the vikings knew perfectly well how to build even the more complex siege engines, so I don't see the point of restricting the norsemen from siege warfare.