Yes, the deep sand bed is really dependant on how the sump is configured..Usually best to go for about 4 - 6 inches of sand, then some small chunks of live rock ( rubble, not large pieces ) on to the sand bed..
And yes, you do need this aswell as the live rock in the display tank..You actually need sand in the main display, a lot of people run the main tanks with a bare bottom, but this is down to personal preference..
Niko