HPM-Board

Each nation gets their own national bank and their own currency that is managed by the Emperor and bankers. Each nation fights to make their currency the dominant currency on the server. People will be able to trade currency for other currencies or for items. Depending on which currency is being bought the most, being traded with the most or being sold the most can alter the currency's buying power.
Inside banks will be a vault where gold is stored. The nation and the people of the nation will be able to buy gold to be kept in the vault incase the nation's economy collapses and the nation's currency becomes worthless. This gold can then be used to buy other currencies that still have reasonable buying power.
Nations may not use other currencies as their official currency unless permission is granted from the other nation. People may only store gold in their own nation's bank or the bank of the nation of their official currency.

/money will bring up all the nations' currencies

/pay [name] [amount] [currency name]

Is this a good idea, or will it make things too complicated?

Too complicated, and the pxl has proven fiat money isnt trusted by the majority of players. As I see it there are two options, either we go back to bartering, or we start using something as currency that is backed by some actually value, like diamonds or emeralds.