I think you would be better off creating an auto landscape material rather than using any additional maps from WM.
Especially if you plan to be able to paint new layers onto your landscape.
There are plenty of tutorials around, here’s a link to a playlist of a great tutorial series on landscape materials: ?v=Kh8F3uUdiRA&list=PL2G_ecHWhZBmEQih1qfe4yIzY49tKxST6
Hope this helps you out, if you have any problems following it let me know with a reply, I’d be happy to help out in any way. =]
Here’s a screenshot of how my material looked a few weeks back.
