They pretty much eat anything. Mine like meatier foods the best, such as bloodworms and frozen shrimp. They readily accept flakes and will eat veggies from time to time. They also will go for shrimp pellets, catfish pellets, etc.
I think they max out at 4-5" so your tank should be plenty big depending on other stocking.
Make sure your tank is cycled completely as they can't take any ammonia or nitrite. Also, be very careful with any medications.