I have not decided if I should have it before the fall of the west or after the west has fallen... Making it start at the begining of Justinians era might be the most fun.
The current project is very unhistorical. I made the Western Roman Empire, Eastern Roman Empire, Persian Empire and Vandals. I made it soo all the provinces in gual and iberia have 9 barbarian level so basicly all of gaul and iberia get overrun with 80k+ barbarians very fun to watch as they pillage and burn until most of it goes back to uncolonised. I made persia really tough by putting 400pops in parthia to repisent off map population and made it so all barbarians types spawn 3x as much. It's fun to play as the east to try and reconqueor the west and vandals while worrying about barbarians and persians... Have some weird crash after about a year during recent tests need to figure out what causes it.
The hardest areas will be leaders, relegions etc.
I was thinking instead of omens could make it appointing a Patriach and make it last 10 yrs or something.