I am going to agree with the others and say that the ammonia is your big problem. I would not add any more fish until that reads 0. I don't think the temp is your problem, mine usually runs at 76 or so and everything is fine. I have also had a time where the heater failed and the temp dropped below 70 and off the thermometer scale. Nothing died, everything was a little lethargic, but after the lights kicked on and started heating things up they all perked up. As far as adding too many things at once, it doesn't sound like you really added that many things at once. I have been bad and added 6 fish at once to a 55 to save on shipping from here and never had a problem. I do a 10% water change a couple days later and then again a week later when I usualy only do them once a month or so, but nothing died or even appeared stressed. I do have about 100lbs of live rock and probably 70lbs of aragonite in the tank with more rock rubble and sand in the sump area too. Plus the tank had been up for over 2 years.