Re gold & mining - I presume that if mining companies are resisting banknotes in favour of their own coins, that indicates that the Commonwealth has abandoned the gold standard (or they'd be having to buy the gold in order to back up the banknotes anyway)?
I like the system, but I think you might have one too many names of coins. I'd suggest dropping the florin, which I always see as a gold coin and would confuse me if it were that low down in the pecking order (and it feels more culturally Italianate where the rest of the names are quite Anglosphere-sounding). If you need something of that denomination, suggestions: "Quarter-crown", "Twyshilling", "Greatshilling", "Greatfarthing" (or call the current "shilling" a greatfarthing and the current florin a shilling).