v11 -> v12 changes were a significant issue making this bot function as they had major API changes between these versions.
discord.js event cheatsheet is useful for seeing all the events in one place
Discord-EmojiToRole had a lot of initial code that was clipped to get this running. It wasn't written for v12, but logically it is pretty solid.
Deploy your bot to Heroku Daniel Shiffman has an awesome tutorial