Food. They'll eat a lot of stuff. I would try to keep it varied and not just feed pellets.
I like Omega One pellets.
Other than that, they love insects and worms.
Tankmates. Lots of options. Oscars, and many other SA cichlids.
I feed mine lots of different stuff. Freeze dried krill, frozen bloodworms and brine shrimp, and tetramin carnivore pellets. i also give them the occasional feeder fish (tuffies, not goldfish) and they are all doing very well
Jd's eat, I mean really eat. I've never seen a cichlid eat more. they'll eat anything unless they are sick. I've had 3 dempseys and they are always the first one at the top for food. hikari pellets work well or flakes of any kind. my current jd 6" male has destroyed a few comets in its day, but I dont like feeding live food all that much. I hear there's too much risk of disease.
JD's are great looking fish and like most other cichlids will accept most foods either prepared foods live foods or pellets they grow to around 8 to 10" slow growing speices they do well with other smaller cichlids such as Firemouths, Convicts and Slavini's you may even get away with keeping them with Cichlids of a larger size such as Oscars which you mentioned about in another thread.
Don't keep them with large fish such as Pbass .... lol ask The Trust why ..... lol