As far as bottom feeders go I went with the assorted snails and hermits . Because my tank is a bit larger 130gallons with a 90 gallon sump I opted for a Hawaiian lobster a manderin goby and a watchman with a couple sand sifting starfish. I found as long as the fish are fast swimmers the lobster leaves them alone
In the case of sand beds I was always told an inch or four stay out of the in between because of gas release so I went an inch in the display tank and 4 inches in the sump to boost the denitrifying bacteria
Hope that helps