This sounds amazing and, as an amateur historian, I really got a lot of ideas seeing this. I don't know how much is already done, but would it be possible to add factions to this like for example:

- Arabian trading cities (like Medina [which was named Yathrib then] and Mekka)
- Sarmatia (horselords north east of Thrace)
- The Alamanni (germans north of the alps)
- the kingdom of pergamon as a separate factions
- the illyrians, Mauretania (around Marocco)
- Nubia ( the Upper Nile, elite archers let's go)
- a kingdom of Cyrene or Crete
- the Belgae and Nervii (northern gallic factions).

Also, maybe you can expand britain and add a few tribes there, for example: make the current southern British faction the Atrebates, little North from there the Catuvalauni (probably the tribe of Cassivelaunus, the opponent of Caesar) and around wales the Silures. The conquest of Britain was namely a fairly tough affair with the Silures being the stiffest opponent of Rome in a good while.
And as far as I know originally the Venetti were north of the Alps, not at Patavium, however I am not 100% sure about that. Not that that would matter a whole lot for the gameplay though.

I am 100% looking forward to this mod, it sound SO amazing. Especially if you can get a long term plan for all playable factions with all it's unique ideas. Boy, have not been this enthusiastic in a while for an upcoming game/mod.

Cheers mate, will help you out with a coffee once my salary is in.