So to start… today ill let you know a little secret, how to get infinite emeralds.
All you will need is a librarian who has a trade for bookshelves and a trade for emeralds. You will have to reduce his prices by simply curing him and then you will get all his trades for 1 emerald/book.
Sell him 1 book which will give you one emerald. Use that emerald to buy 3 bookshelves. Destroy the shelves and you will get 3 books out of each. Repeat the process until your happy.
You can thank me later 🙂