As for which species of benthic sharks is best to keep.
It's really about you personal preference & what you ultimate plans are for the sharks and the pond. By that I mean - do you just want to keep a mini-natural habitat, or do you want to breed them. Also note - each species has their own personal charms & beauty.
As for buy them as eggs - I wouldn't recommended it unless you have some experience hatching & raising sharks. Often times - there's difficult in getting newly hatched sharks to feed, which can result in the pup dieing.
Your actually much better off getting a pup that's a few months old - basically 8-12". At these sizes the pups are much easier keep alive - since they've already been feeding. And will most likely eat with in less than a week after being placed in your tank.
As for tank size - there's many opinion on this. Some claim you can keep pups of these species in a 50 gallon tank. But since the plan is to keep the pup in a tank until it about 18" long. You want a tank that in the 150-180 gallon range(basically 60-72" long x 24" wide).
After what temperature to keep them at - again it depends on the species.
While the Bamboos, Epaulette, & catsharks(Coral/Marbled) general do best between 72-82F. The California Horn tend to like waters that's slightly cooler in the 65-75F range.
