We frown on nothing except discourtesy! Welcome to the Guild!
I don't know anything about World Painter, but based on your request, I assume it is based on heightmaps? There are a number of possible approaches. Some people like to stitch together real world height data, since it's guaranteed to be "realistic." A good place to start looking for that his here: The National Map: Viewer and Download Platform
Others prefer to use entirely synthetic heightmaps. There's a program called Wilbur that's pretty good for that kind of approach (don't worry; it's free!) Wilbur's author is a contributor here under the handle Waldronate, and he's very helpful. The program and some tutorials in its use are available here: Current Wilbur Version