Hi TheMonk, thanks for your thoughts.
1. Is the chinese coins really necessary?
No, not at all. I encourage people to use whatever coins are used in their respective country. Although personally I use the ancient Chinese coins.
2. Are mixed coins bad?
A European client uses the same 10 cent Euro coin, but two are Spanish coins, while the third one is an Italian coin. The divination result does not seem to be off the mark. I haven't had enough experience with mixed coins though, because people easily come up with identical coins.
Mixed coins can still be used, because they still give the Yin and Yang representations.
Can you not simply know that you require one side of a coin to be represented (represnting yin or yang or whatever is needed) and simply go along with that?
Yes, we can!