I agree not all civs should have a colony, but certainly empire building civs should have one or something similar. And Rome is the quintessential empire builder so it is a reasonable suggestion that they have something along those lines.
Regarding veteran Triarii cost, I say it ought to be left the same. Skiritai are a sword unit, so not a direct comparison for Triarii which are spearmen, which don't cost metal unless champions. Rome already has swordsmen, adding another metal cost means Rome has no melee infantry in event of a metal shortage and that is unacceptable from a game play viewpoint.