Made an Island in world machine - I think I am happy with it but now I need advice

Hmmm, sorry, I am baffled now. I would have thought I could have done the following :

  1. Create world in world machine and export to unreal
  2. Create (or buy) various rock meshes and import them to unreal also
  3. Place them strategically along cliff edges and terrain do add more detail
  4. Do the same with trees and grass on their respective area of terrain aswell

If this isn’t doable, then how do games companies add detail?