cory cats are not the best fish to fish in cycle with, but too late now.
Stock (number wise, and considering the bioload) is pretty good for a fish in cycle.
Try fasting once a week, and make sure to feed lightly. A 50% water change wouldn't hurt to get the nitrites down to .25 ppm
Just FYI those serpae tetras are going to make it a bit harder to stock the tank.