Sand tends to look more natural then gravel does,and yes you could try the effect, without the divider, I did it with my tank ending with a large rock overhanging (Made a nice cave for my ropefish) If you do it right, it can look really good, I used play sand, river rocks for a hobby store, and some larger rocks to help hold up the outcropping. If you want any bottom feeders, go with sand, it tends to treat them better (Gravel is sometimes to tough, and can scratch) live plants like sand better, but a layer of gravel underneath, though a little more work, will help the plants to root themselves in. As the people before have said, a common Pleco will get to large for your tank, they can get up to 1 foot long. Bristle nose plecs don't grow nearly as large, 5-6 inchs.
Side note: I made a strainer out of a coat hanger by benging it into a large oval, so when I run it through the sand, the gravel or river rocks stay with it. Make sure the gaps are small enough that the gravel doesn't go through.