Other than the worms, the best food would be the commercial frog food. Often ADFs will eat non-living foods. They will eat a variety of freeze-dried or frozen worms too. Minced meat should not be given due to the high fat content.
It is best to use a substrate. You can use sand or gravel. Make sure you have a good undergravel filter and provide plenty of hiding places. A variety of aquatic plants would make an attractive aquarium. They do not damage the plants.
A single frog is OK. Frogs are generally not very social except during breeding time. However ADFs can live quite well in small groups. You can put 6 frogs in a 80 liter/20 gallon tank.