well either late ancient or early classical. I would give a salt mine a commercial bonus rather than production. It's not like salt helps in production... but there was a lot of commerce of salt going on. About which luxury to add in the Anno Domini age... well I'm not sure, especially since I don't know which all other luxs are

In the Rise of Rome age I would put marble, if not before.
About which Civs to add... well it depends from what you want. If you want to fill an hypotetical geographical map, or if you want to be original and put civs other mods like TAM didn't, etc...
Btw I would rename Celts as Gauls. Because Celts is a very general term... and you have other celtic civs in the mod. Vercingetorix was Gaul

About Rome... I would never choose Trajan as roman leader, sigh sob. I would have picked someone more political, he was more of a military leader, that's why the helmet in your LH fits well

. But I won't insist too much, or Xen will become mad and start a kilometric thread
Psycho, most european and middle eastern populations came from caucasus or mixed with caucasian nomads. That's why the race is called caucasian.