A Chariot would be very cool, but the one thing you need to understand about chariots is that they are very unstable. They are almost exclusively for use on completely flat terrain. any bumps in the road or declines over 15 degrees from side to side would usually tip the chariot over. Its not a tank. its a fast and mobile skirmishing platform designed to soften up the enemy ranks before the infantry gets there.
the 4 person comment above made me chuckle. most war chariots were 2 man. driver + archer or spearman.
It would actually be cool for someone to be able to purchase a chariot. he would also have to have riding skill, because he would need to buy the horse that pulls it. thats right. it shouldnt be a single package. horse + chariot in seperate purchases. if you cant ride the horse, it cant pull your chariot.
this would make for different classes of chariots. with differences of speed (determined by the horse you buy) and differences in manuverability and stability (determined by the chariot you purchase). It should be a 2 or 3 slot item like a siege ladder, that pairs with a horse. and when you deploy it, a team mate can climb on with you by pressing the f key. Lose your archer?? just go drive by and get a new person to climb on with you. This would be really fun
But they should only be usable on specific maps. like the coloseum maps, for instance. or some flat plains maps.