Neolamprologus ornatapinnis is a not really common one that's nice looking. They don't actually live in the shells so much but do use them for breeding. Females tend to use the shells more. 1 male to a few females is best. You wouldn't need as many shells that way. Technically drop the neo in the name.
Ocellatus is a good one too more of a shell dweller. Heavy female ratio again though. But that is with alot of "shell dwellers".
It depends on which shell dweller you want how many shells to get. Multifasciatus like them in two layers...piled up. You might want to check availability...they are not all available at all times.