Marty,
a 50lt tank would be enough for 4 fish (2 pairs ) with good filtation and reg water changes.
The fry are just under half growen, but will need lots of food every day to grow to there full size 12cm.
As there big eaters I would not use gravel. If you did it would be better to have them in a larger tank that could handle the unseen waste(hense better to have no gravel).
they are carnavors, so anything meaty is good, good quality flake, beef heat, boodworms, medium garden worms, mozzy riglers, water fleas, small fish any thing you can think of.
I've grown them fast so you really need to keep up with there needs or when in 10 months it comes time to breed them the females will not fill with eggs readly, making it harder to have a succesful spawn.
don't know wether I'll be able to get the fish to Caryl but will try.