I suggest you take a look at the Minecraft terraforming community, as a lot of them use World Machine to create very exquisite and complex terrains, with multiple biomes. Check out @Consue_IdeaGen (@Consue) on twitter for example. Her is a render of one of her many maps:
As for creating a basic crater, here is an example of an old one of mine:
You could easily create one that’s 32 Km in size and create areas within. For example, this crater has three “layers”. The bottom, the slope with some rock and a lot of sediment, and the cliff edge. You could add an arbitrary number of transition areas, to your liking. It would be a multi-biome map, just placed within a crater.