Dwarf puffers (sometimes called pea puffers because of their size) are MUCH better off in their own tank (1 DP per 3 gallons) because even though they are small, they are VERY nippy fish and are VERY territorial. Do NOT underestimate their size and cuteness! Also, because they are slower than most fish, they will not be able to get to the food fast enough before it is all eaten by the other fish in the tank. These fish are NOT a community fish!
To answer your question on what they eat: They'll eat frozen brine shrimp, mysis shrimp, bloodworms, live snails (it's fun to watch them hunt snails), and most other frozen fish food.