Well if the tank is fully cycled there should be no ammonia when adding livestock. I don't think you could have too much bacteria in a tank, but I guess if it all died off at once it might cause an ammonia spike. I think they say add a little bit of fishfood because you don't want to dirty up your tank too much. It is possible to have too much ammonia, but I don't think i've heard of anyone who has added too much while cycling so I wouldn't be too concerned if I was you