Copy the RTW stuff, and save it elsewhere, that way you have the basic to fall back on or play. You will have a separate exe. I believe you are supposed to have a clean version of Rome, what that means I am not sure, I took it to mean no saved game, though I don't know. I do know that because I had a copied RTW file, I could play either RTW or EB, so I don't think you have to clear your saved games. Two downloads is right. It is a bit unstable, meaning more crashes. Don't be frustrated if it gets to a point where everytime you try to end turn it crashes. Most of my EB campaigns hit that point eventually.
Parthia was a well-kept secret
So you are doing well for money? That is what killed my Parthia campaigns. Early on, how did you deal with chariots? Just curious for when I start one with Parthia again.