Re: Fantasy coinage
I'm gathering a number of notes into one post:
The first method (though note that sometimes full-face representations were used) is what was used from ancient days through the 17th and 18th centuries (and later), save for the US and other republics. After all, the right to coin was considered part of the honor & power of the monarch, hence his visage "should" appear on the coinage. Putting a dead king's face--much less the face of someone who isn't and wasn't and won't be the king--on coins makes no sense in such a POV: the coins should uphold and increase the honor of the current monarch, is the idea.
The royal coat of arms is an appropriate reverse for the major coin(s), elements from the coat of arms would work on lesser coins, and various symbols (not necessarily from the royal arms) would be OK for minor coins.
BTW, the value of the coin was often written on coins, even in periods when the majority of citizens were illiterate--after all, the royal ministers and such were largely literate, who cared if the people weren't?
Actually, in ancient days a 12:1 ratio was considered standard, indeed "proper." The 20:1 ratio is about what was found in medieval times; even then it could fluctuate a good deal. Also, that was what you'd find in Western Europe; it could vary elsewhere (e.g., in early midieval Arabia silver was more valuable than gold!)
You have listed a number of different coins. However, there are only three units of money; pounds, shillings, and pence. This is similar to the USA, where there are dollars and cents, vs. pennies, nickels, dimes, quarters, half-dollars, and dollar coins (plus various denominations of bills). Also note that, just as cents are units and pennies are coins in the US, pence are units and pennies are coins in pre-decimalization UK. BTW, the biggest objection to decimalization was not that it was complicated, but that there was no way to evenly divide a shilling (or a pound), by three.
I think it a good idea here to touch on the subject of "money of account." Through the Renaissance (and even beyond), most accounts were kept in terms of a unit of money that was seperate from any actual coinage. That is, one would write down an expense as so-and-so many whatsies, regardless of what coins were used to make the purchase. In an era where the king might suddenly issue the most debased coinage imaginable, &/or in a society where one could be faced with coins of wildly varient value and purity, a way to keep accounts that was independant of such "external" fluctuations is obviously a marvelous idea.
Thus, accounts were kept in a steady, dependable unit of money, even though that unit was fictitious. In England, for example, accounts were kept in pounds/shillings/pence from early times, even though no 1-pound coin was issued until the 15th century. Further, one might (for example) hand over 6 shilling coins for an object, yet record the value of the purchase as 4 shillings: this would happen if the money was debased.
BTW, in Spain the money was the maravedi, yet (so far as my researches have ever found), no such coin was ever issued (not surprising, as it was a very small value).
Thus, a money of account helps to compare one coin (or coinage system) to another.
Obviously, the idea of a money of account could be a very interesting addition to a fantasy campaign. It would help the GM show the players the sort of complications that realistically would exist in a medieval-like setting, where coins from all over would be flowing in and out of the city (or wherever the characters are headquartered), and people would need to be able to convert values of varying coins and coinages.