Question? Is Rise of Rome just a cool name or will the campaigns be the rise of Rome? If the latter is true and the campaings allow unlocking units as goals are achieved, than that will really make for a good storyline.
Start with simple units and unlock more advanced ones as the campaign goals are met. Though I find it hard to speculate how to "make" things for BFME without enuff source material.
How would you model anything without any source models to compare it to? Can't ini code till the game is released. But I'm glad you're doing the homework of research to prepare. I will be watching the progress on this one as I'm a fan of the idea.
