Yeah, I’m afraid there’s no fixed way of doing this…
If you’re going to set up a single terrain, then you might as well use the Epic tools to do the foliage.
It’s only if you want a strictly procedural map that you need the kind of approach you’re looking at. If you want things popping up at close range this is the way to go.
As you are / might be aware, you can have more than one landscape. You could also split those up with streaming volumes, just thinking out loud here.