I use a similar technique, but with a couple of variations.

First, I do not remove the surface of the cork bark to make a depression. The texture of the surface is far better for the plant to sink it's root cells into, gaining a "grip" on the mount.

Secondly, I never put moss under the roots, but only cover them. I have noted that the roots attach to the surface far more readily that way, rather than growing into the moss pad.

As to mounting multiple plants together, generally it is best to keep them as individuals, so that if one plant becomes infected or infested, its more difficult to "share".