Landscape are a very special case asset inside UE. It requires that you understand its limitations and all the features before planning your scene/game. I have done several landscapes in external tools generating heightmap to import inside UE. The tools which can generate the tiles for world composition are a must at your arsenal of tools. Up to now, I would suggest every user to understand and use world composition regardless of the scene size, because as you make the data outside UE, you can easily change and import back without much trouble, second because the increased resolution you can have for each tile will avoid/greately reduce geometry artifacts with dynamic shadowing.
I would go for the stream mentioned above and any other stream you can find at Youtube about this.