I recommend brickgames or the cashgen plugin.
Brickgames provides nearly EVERYTHING for a minecraft-style editable cubic world, whereas cashgen features SMOOTH and EDITABLE voxel terrain, which might have been implemented using the marching cubes algorithm 
Both of them feature infinite terrain btw
So, it depends on your preference
Plus: I’m also making a voxel project which features infinite terrain, basic ai units, biomes, lakes and so on. I haven’t uploaded the source code, but if you’re interested and want to follow my progress: GitHub - DXGatech/Voxel-survival-primitive-UE4: This is a large-scale UE4 project, made to demonstrate how a voxel game can be implemented with UE4 and Instanced Static Mesh Component