Knowing how big i need to make my game world

It is an option, you just need to be ready to delve into code when issues arise. My game is currently about the size of Skyrims playable area. I use World Composition, and constantly stream data in and out of memory to ensure the world remains persistent. A lot of what I have got for the game is C++, very little Blueprints. So if you are not ready to dive into C++. I would consider an easy genre.