I will bookmark this for further read, but counting: You are overthinking this. Toady hasn't made it this far for half of your ideas to even come into effect, but they will of no doubt be useful in the near future.
Also, money is imaginary. It costs too much money to make it real, much easier to show it on a computer screen and transfer it in exchange for goods. Capitalism, Ho! Also, large scale economy fails. We are already proving that as we speak, local economy is where it's at.
I know, but I want DF to be that AWESOME! It can be, it has potentials (I'll explain below and you might agree as well after that)! And since suggestions are for the future, we do need to think ahead (Probably in my case a little too far, since I already been traveling this path far enough), and we need visions ahead for the future, like every good dwarf should XD
For monetary systems, first, a economy system doesn't always involved and required money. There are economic system like gift economy, which they do existed in hunter/gather societies (with people less than hundreds). But the strange thing is one way or another, it seems every economy system till so far, all evolve into monetary system, and most commonly using 1 and 1 only medium of exchange. Isn't that sound strange enough for anyone who are curious? So we do need to find out why that happen in economics. (There are already many theories/models, and even put to test)
The second part about the scale of economic society. I'll list a real example and a simulation/model that gives you the idea of the scale. If you read some economic articles, the famous stone money may ring a bell to you. (Rai stones was used on a small island Yap in pacific ocean, and local people used these giant sized stone, weight tones and stood meters with a big hole in the center, to exchange goods.) What you probably don't know is the size of the community (who value giant stones as money), there are only thousands of them on Yap, and probably only hundreds when it is used. Even combining the surrounding islands who participated the exchange, no more than tens of thousands. (Till today there are still few people lived there, because they are indeed tiny islands).
Next I'll use a paper - which I have in my hands - Peter Howitt, Robert Clower, "The emergence of economic organization", Journal of Economic Behavior & Organization, vol 4, p55-84, 2000 (Yes, I do reference it in my essay). The system is simulated using a parameters of 2,160 transactors, it is "barters" and a unit of production (or you may just called it an entity as in DF). 10 kinds of commodities, 200 tiles of space (the locations people can trade like a local area in DF), etc. (Don't you think it feels very familiar since it almost the same and within the range of the DF parameters) And monetary-system/market-system emerge from this simple setup and community from micro level without any pre-existed planning. Not always as the results the authors indicated, only within a certain range of variables, mainly it is the overhead cost differences of commodities during trade = f(i). And almost always it evolves into a system using the commodity(s) with a less overhead cost using as a medium, but not always the least one. And most often the ONLY one, even in system stabilized without the only one, (some barters remain bargaining), there is a dominate one.
NOTICE : One of the very basic differences between bartering economy and the one using commodity money, is that the price asymmetry (called the exchange ratio between commodities in bartering, and if one side is a commodity money, then its number of units to the target commodity, still the definition of ratio, will be called a price as we are familiar with). Let's assume you can buy 2 commodity-A's with 1 dollar, and $1 for 3 B's. So the exchange ratio of A:B should be 2:3 in commodity money system. But in bartering their isn't a medium, assuming a gem is in the role of money in previous setup, and A as a weapon, and B as an armor, 1 gem for 2 weapons, 1 gem for 3 armors, but then it's anyone's guess how many weapons for a armor, maybe 2:3, maybe not, it can be any ratio. that's why it's called a bargain. So don't think if you invented a round and shinny object called a coin, it will automatically become a commodity money. It's still bargaining every where, until something happens making the coin (or a gem) a medium as the function of money. Although not fully functioned as we used to in modern tern, from commodity money to metallic, to representation, to paper(credit), to inconvertible, to fiat, to electronic. They all have differences steps by steps. We've come a long way for thousands of years in developing money system. (You can see why monetary and banking are such large branch of economics, and I am not even major in it, so much to learn
)
So I think DF is NOT too small to have currency, but almost perfect in size for monetary system. (You can see why I am so enthusiastic about the economy in DF, it's perfect for experiments, MUWAHAHA
) If it succeeds, maybe I can even reference it! And even if it fails, we do need them to fail in order to find out what makes them tick and analyse it. A system with 100% success is NOT right at all, it may indicate it's planned not evolved. Again, it's FUN makes it good. And I want to post a thread, just to say how AWESOME it can be! (Sounds too TROLLISH for my taste anyway)
About capitalism, and it's "failure"? Again, you lived quite well today, isn't it? probably much much better than anyone on earth a hundred year ago. And the economic system evolve over time with up and down, we even name them as 'economic cycle' you can google it. And the economics right now are probably self adjusting (we called it shakeout). Until it reaches the next equilibrium.
Too much information? Welcome to the world of economics.
P.S Money isn't imaginary, look down in my signature. Money is not excessive, but a necessity. You can't live without it in current economic system.