I think you would get more enjoyment out of your aquascape if you try to incorporate some caves, holes, pass troughs etc. I started with a wall of rock look, and I am happy that I switched gears and started to bore out holes and create ledges in my structure. I think it will be so much more interesting when you have fish flowing through your structures than just in front of them.
after looking at alternative reef, I would stick that big rock in the middle and suspend it using a pvc and eggs crate light grate. You can cover the pvc with stonefix and have the big rock about and inch above the sand bed. Then I would get the overflow cover pieces from Alternative reef of cover the overflow. Leave the rest of the tank open. Check this guys build out Lasse is really doing it up.

