If the LR
came from a dealers tank, and had been in that tank for a while, there probably won't be any die off to speak of. The rock is already cycled. The LS
you got isn't really LS
except that it should have live bacteria in it. The sand stirring critters that you'll need to maintain the DSB
are not in there yet. I would, if you can, get a cup of sand from an established reef tank and add it to your tank. If that isn't an option, you might want to get a detrivore kit from one of the online dealers. Before I go any further with that, how deep is your sandbed? How much LR
do you have in the tank? Have you checked the water parameters? Ammonia, nitrite, nitrate, pH, alkalinity, salinity... What is your ultimate goal for this tank?