First make sure you have a brackish water tank setup....mix of salt water and fresh water. They can live in fresh okay, but not for very long and will most likely encounter disease problems etc if not kept in the correct setup.
A fine substrate like sand is best since they are filter feeders and when young they could choke on gravel....usually once they mature and are of a good size then they should be able to dislodge any gravel that is ingested by accident.
As far as feeding, target feeding them is probably best that way you know they are eating...use a turkey baster or something similar to get the food close to him so he know's it's there. Feed right before you turn the lights off as well...he will most likely be more enclined to eat when it's dark and feel more relaxed. Frozen and live foods like bloodworms, brineshrimp and beefheart etc are some good foods to feed him. Some have been said to eat shrimp pellets, but honestly I dont know how true that is....some might eat them I guess, but for the most part they wont.
They need a fairly large tank as they can reach sizes of about 2 feet or so. They are territorial towards each other and can harm each other pretty bad as they have teeny sharp teeth.
They are not aggressive when it comes to other tank mates...maybe towards other bottom feeders, so make sure he's the only bottom dweller to decrease the chances of any fighting.
They can eat smaller fish, but usually only if they are sick and dying or dead on the bottom. They are not hunters so should be safe with smaller fish.
As far as tank mates go, house the dragon with peaceful community fish that aren't nippy or aggressive. This means no cichlids since they can be real nasty fish to slow moving fish. Dragons are easy targets to get picked on as they just lay on the bottom of the tank or hide under/in decorations majority of the time.
Hope some of this helps you out some. If you have anymore questions, post away!

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Good Luck and keep us updated!
Candice