For the displacement problem you can try adding a subtraction math node to the displacement. This will make the displacement go down instead of up.   As long as the displacement map was made with pure white as the maximum displacement it should work with no problem.  If however the maximum displacement is represented by a shade gray you  need to change the subtraction value to account for this.  For example if the maximum displacement, or lightest shade, is only 50% gray the you would only subtract 0.5

In the picture I'm attaching the plane on the right is using a typical displacement setting while the one on the left uses a subtraction math node.

Chris Cox