I agree with OP. The OP didn't mention the particular needs regarding a positive current in the water, suggested number to strive for in the known schooling species, proper cover, and, not the least, keeping your hands out of the tank, ALWAYS.
I have personally experienced the sharp end of these beautiful fish and that alone keeps me from keeping them again. People I know that are currently keeping Piranha are divided between excellent and irresposible. When provided with proper care these fish flourish. When kept solely for entertainment, proper husbandry often takes a back seat and the fish suffer.