Might be a problem, since I don't think there are any mods for the era before Persia's rise. Try having a look at the RTR forums or the Total War Center for a mod that would suit the timescale. Then you have to decide whether it's a traditional PBM, ie players switching reigns, or Myrddral's new type, one where each player controls a faction. Then you'll probably have to set some house rules, to avoid winning too early so only a few people can play, and to make the campaign more interesting.