They like sand, but gravel is fine.
If you are keeping more than one, the heavily planted is important, especially as they mature and begin claim their own personal space.
Nothing that they like to eat is particulaly easy to store unless you have a freezer, as they will almost never eat flake or pellets and need to be fed live or frozen small invertibrates such as bloodworm, brine shrimp, mysis shrimp, microworms, daphnia & cyclops.
Also live snails & snail hatchlings are an important part of the diet to maintain dental health.
Occasionally some will take dried versions of these foods but this is rare.
How big is the tank? With Dwarf puffers, the 'inch per gallon' guidline doesn't work. Each fish needs a minimum of 5 gallons in order to establish territorial space. Any less and they will start to kill each other as they mature, although to start with as young fish they may seem peaceful.
Suitable tankmates are limited to armoured catfish such as bristlenose plecs and small freshwater gobies.