it happens to the best of us. I killed my 1st fish. I had a chromis, and I fed it. A piece of food feel in a wedge in a pice of my lr. And when I woke up the next morning the fish was stuck in the rock what appeared to be trying to get a piece of food.
Anyway, when your ammonia goes down, your nitrites will go up. then when the nitrites lower your nitrates will go up. Whne your nitrates start to fall then you will be safe to add ONE FISH at a time. If I were you I would order my fish over the internet. For what you are paying you can get a much better deal, and healthier fish from a site like SWF.
Buy a test kit, and test your levels. Don't do any water changes. When the nitrates start to lower, then you are ready for fish. Could be a week or two.
HTH
Leopard
PS if you have any question what so ever DO NOT be afraid to ask. the dump question is the one not asked.