I looked at the source poem once more and considered the fact that it was inspired by the California Gold Rush. I remember Alan, during his feedback of my presentation, first thought that my story took place in the wild west, so I thought to consider actually turning that into a reality, since it would make much more sense as a setting in relation to the source material and its origins than a victorian England backdrop.
In terms of characters, I would now much rather prefer a smaller cast of characters instead of a zoo-full. The hero of my story would baybe meet up with these characters along his journey to Eldorado, instead of all of them turning up at once at the beginning of the film.
Western movies often give the feeling of adventure and dangerous quests for a MacGuffin. In this case, the MacGuffin would be the Golden City and riches beyond the hero's wildest dreams, but the hero would eventually see he must use these riches for the greater good, or maybe realise that some things are best left undiscovered and unspoiled.
Old west small/medium-sized animal examples:
I'm heavily leaning towards a squirrel for my main hero, either a snake or vulture as the villain and the shrew as the intelligent bookworm sidekick.