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.

The game's fundamentals have definitely been altered. It's easy to build branches that can then bypass defenses and reach the Civic Center. In theory they should hold up, but not that much armor.

If it's like a pirate society but on land, some groups are just as aggressive as a wasps' nest, while others are simply aggressive.  But these are societies that can easily create an army. I remember reading about the Gallo-Romans; having many Celts in their composition meant they could have levy militia troops, and this was true even in the Middle Ages.