Customer Prefs lets you add Receivables Categories that you can select for Customers.
For Currencies, you add a new currency on Company card and to use with customers, create an A/R account for the currency and add the account to Receivables Categories.
Pictured, the new A/R CAD, receivables account in Canadian Dollars, has been added. When a new Customer is created using CAD, the matching A/R CAD can be selected.