I have kept several of the Lepidiolamprologus species: kendalli, nkambae, hecqui, cunningtoni, and attenuatus, with the longest term keeping of the nkambae species.
If the L. elongatus lean towards L. kendalli and L. nakambae in their behavior they will be very aggressive to conspecifics.
Probably best to get a group of youngsters and let them pick their mate as they grow. Be ready to get the fish that are pinned in the top corner out of the tank...they have been asked to leave

IMHO, a 6' tank is best for adults but you might get lucky keeping them in a 48"x18" footprint.
If buying them small, be sure they are the right fish because elongatus, kendalli, and nkambae look nearly identical as juvies.