I don’t know if there are actual hard limits for level size in Unreal. What I know is that if you get too far from the origin, you will lose precision in the location of objects because you start losing decimal places in floats. The farther away from the world origin, the crazier things will get (it gets buggy).
You should do a test. Create a floor the size you need and put some objects and the player and run around the edges to see if it gets buggy or not.