Finally, I'm making some progress. Tonight I began building the rock structure that will divide the middle "plain" section from the left stem section. This is the left rock structure that I put together at my LFS. I modified it a bit by rotating the main rock to show a more detailed side, as opposed to having that side fact the top of the tank:
This is a 45-degree rotation to toward the middle of the tank, showing the cave that I built into the design, which should provide a comfy home for cave breeders (I'm thinking of getting a pair of apistos).
Finally, this is the opposite side of the structure, which is kind of empty.
I'm thinking of adding some rock to flesh it out and close off the other end of the cave, but at the same time, it faces the back of the tank, so no one will see it. Let me know what you think about adding more rock.
For those interested, I used the cigarette filter and crazy glue technique to glue the rocks together. I will go back at some point and glue crushed rocks over the exposed filters to hide them. It only took about 10-15 filters to firmly hold the structure together.