I have not read the whole thread, just the first page, but here is my suggestion:
First, disable villager trading (or at least change it from emeralds to something else.) If it is left in, people will just be able to farm currency which will severely fuck the economy up.
Next, when the map is pre-rendered, place emeralds in the ground in the same way all other ores are generated. This shouldn't be hard to do, just reverse-engineer the other ore spawning classes. You could set the rarity and vein size while doing this to balance it with gold (if gold is kept as a secondary currency).
Honestly though I dislike the idea of using emeralds as currency - gold has always been the symbol of money both in real life and in most RPGs.
The main point is - take emeralds out of villager trading. It will cause hyperinflation as more villagers are exploited - eventually making emeralds completely worthless.