1. Why are you using crushed coral, and if you insist upon it, it doesn't need to be that deep.
2. Drip loop. Your power strip should be mounted above the floor of the stand, and the power cords should come down past the power strip, then make a small "loop" (better yet a "u-turn") so that it comes back up to the power strip. This way any water flowing down the power cord, cant make its way to the power strip.
3. I am not concerned as others about the overflow box, properly set up they can run for years without a problem. I used one for six years without a problem. Your milage may, and probably will, vary.
4. Go pick up a twenty gallon tank to use as a sump. The rubbermaid you are using looks like it will fail, if not leech nasties into your tank water.
5. To take care of the return pipe from your overflow, take a sufficient length of PVC with a diameter larger than your overflow pipe, and insert the over flow pipe in one end, and put the other end of the PVC in your sump so that it touches the bottom of the sump. This will prevent it from spraying water all over the place. To avoid back pressure, cut the end of the PVC pipe that is in the sump at a 45 degree angle.
6. If your overflow can't handle the water being fed to it by the pump, your tank will overflow all over the place. Either restrict the pump with a valve, get a smaller pump, or a bigger overflow.
7. Don't keep your artwork behind your tank, it will get ruined.