Money will be rather straightforward in Valley of Blue Snails. I don't care to use alternate currencies much and 1g = 10s =100c is pretty easy to remember. I probably will not use platinum except for jewelry. Value is by weight and purity, most actual prints on the coins are interchangeable in most locations. Dwarves in particular are fickle about purity. Dwarves may also alloy their gold and silver with other metal to keep them safe, then separate them at a later point.
Large denominations are usually not passed along often since they are things like plots of land, houses, titles and so forth. When they are gold bars could be pressed to weight, usually 250gp or 500gp. Peasants usually do not deal with hard currency and favor to barter. If they do have coin it is usually a small amounts to be used in dire times. Merchants and nobles use coins often and also write each other writs of property, value of title. These writs are stamped by the local lords and are essentially a written contract to be fulfilled - breaking the contract is punished harshly. Peasants and the like would never come across such a writ.
The PCs will likely have both coin and barter material. I am fond of non-coin treasure, should it be furs, gems, arts, pottery, narcotics, wines, noddles, harlots, jewels, trained squirrils and so forth. PCs could easily barter this among the general populace for whatever they need. Money can buy just about everything - land, titles, wives, slaves, assassinations, children and just about anything else. Most noble lords will tax excessively and PCs had best be wary if they intent to simply take on a huge load of treasure and walk away without paying the local lord his due. I will leave this part vague for now since it will certianly vary from place to place heavily.
As a side note training is a matter I'm considering when a PC would level up. Adding a cost involved seems to be a time-honored tradition although I'm fairly apathetic to be honest. My main interest is to keep some role-playing value involved for major occurrences. Lets say if a 2nd level Fighter picks up a level in Thief. Clearly some role-playing would be involved, and likely an entire adventure. Normal in-class leveling I will likely keep it as DM fiat. New materials will need to be bought, time to train will be devoted towards and so forth. Loose figure, 20g and 1 week per level - hardly something to worry about in terms of breaking a PCs bank.