The forums is the best place to get this kind of advice. As a starter, you can use something like World Machine to create heighmaps for your terrain and then do further tweaking in the editor. If you are planning to make caves, then you’ll have to model them as static meshes. You can get more detailed information in the forums.
Ok, I found info on how to stream a open world game using UE4 but…What program do I need for World generating?
On top of that, I need to be able to dig say (2000 feet) into the earth…SO…What program can do this? UE4 OR Do I just make parts in Maya.?