Landscaping isn't too hard by mouse as you can control and work it how you want. It takes longer, but you make it your own. The real life data import looks good!
Foliage can be a pain when dropping something new in to use, where it takes a billion years to load into the foliage editor. I do agree with grass making the game look much more realistic, same with particle effects and more.
Crashing in UE4 is very likely at times unless you got a really good PC, but the fact you keep sticking with it is one of the best steps in making a game.
I’m just glad I didn’t have any crashing in the first level I built. That went rather smooth and let me get familiar with using Unreal.