Well apparently this thread is already about trying to get units that both try to not overlap, and still manage to move around in groups of 50 without too much weird stuff happening... 

Written down in their present form in the High Middle Ages. Even if they refer to supposed events from a millennium earlier, it's hard to know by then what external influences and other anachronisms could have crept in in the story (as I've recently mentioned happens with funerary practices in the Iliad, where half that time passed).

They are apparently mentioned in epics https://celt.ucc.ie/published/T301035/text021.html https://celt.ucc.ie/published/T301021/text086.html Now those might just be exaggerations, which does bring into question how accurate other passages about chariots are. Although i think the Irish may have actually had chariots (but probably not with blades), as you have mentioned before in the thread there is evidence in some metal fittings and their word for chariot.  

Is minimizing overlap important for the momentum/pushing? I think much like for ships, we will have to allow an amount of overlaps for the sake of pathfinding. Otherwise, you might get results that look good on paper but that can end up quite frustrating in practice.

Furthermore, the Old Irish carpat (ˈkaɾ.bəd̪) for chariot can only be derived from a Celtic language. A borrowing from Latin would have resulted in a completely different form and pronunciation.