I don't love the idea of different currencies, but if it were feasible, I wouldn't mind too much either.
Money doesn't have to be bulky, though.
Depending on era and country, coins could be as large or as tiny as inflaction dictated.
Besides, it has been already pointed out: "denars" can be considered a symbolic currency.
They could actually be gold or silver ingots, with no special value beyond inherent metal value.
It happened; fines for deserters, in Carolingian times, used to be paid in gold.
And since golden currency was nearly unheard of, we must assume laws meant unsigned gold, that is, ingots and bars, at face value.
I wouldn't mind a barter system - it would make sense.
Nor I would mind a complex monetary mechanism too much.
But M&B is first and foremost a fighting game.
A fighting game without a gaming world.
Before asking for details [such as detailed currency] we need the general framework.
EDIT:
I must be missing posts; when is next version due, exactly?