Melody,
I use argonite live sand. We don't have any of the Southdown sand here in Miami. But, if we did here is what I would do. I would get enough Southdown sand to make about a 4 inch sand bed and seed it with some LiveSand. Then place the LR.
If you don't have Southdown get the Argonite oolytic (sp?) and seed it with LS.
The other thing I would do differently is get a Metal Halide/PC or Metal Halide/VHO combo lighting set up. I have 2x65 watt pc now, which is okay, but the MH's would enable me to get corals which require more lighting.