For physics, the limit is around 6km, so for safety it’d be good to do it in 5kmx5km pieces.
Beyond a certain point, the numbers become too big to have a high enough precision (due to the kind of variable that the values get stored as) and so things like movement and physics have problems. That’s why there’s world composition and origin shifting, where it moves you back to 0,0,0 so that the numbers are low again.