PAFC: Hi there, I'm new to this game & forum too, glad to see a newbie like me around too

Anyway for the first question, playing other factions are only possible only after completing the Imperial Campaign once through

The second question, using the Diplomat right-clicking on a stack that has a general will open up a window. On the top of the left, there's a bribe option, select to bribe the enemy. I know this because I tried it Bribed a Brutii family member