I think the first question should be, is the currency debt based or equity based? We currently have debt based. And in reality anyone can start their own currency, any time they want, using the current rules. Many-o-times I thought the federal reserve needed a competitor. But to answer your question I would say yes it can be simulated on a computer. I would imagine it would be the same as using a single country.

Before we go there you perhaps want to answer this - what in your opinion is the function of banks and of currency?

If there's a single currency, who gets to set it's value in terms of goods that it can be exchanged for?

If there's a single bank what is its function?

Most probably this: Someone would create a second bank and a second currency.

There sort of already is one bank, IMF