Not sure if I read up above, but does the cave have a purpose? It feels quite artificial that it is facing directly out of the tank. I would adjust your front line of stones so they are not completely straight. Maybe adjust the entrance to the cave so that it is not perfectly perpendicular to the glass.
I've had and idea to do an edge of a Forrest like this, with carpets on one side and Forrest on the other. But I agree that it looks like two separate tanks. If you built up the Forrest so that there was a small cliff between it and the grass, that migh provide rational for how these two different ecosystems are directly next to each other.
The dragon stone could work as a small mountain but I would be tempted to either leave it out or break it up to smaller pieces and make it more jagged and less uniform. Not sure though