I agree with the others, leave your tank alone with no other livestock additions for a month to 6 weeks and let it settle in and mature a bit and see how things are doing.
When adding livestock you have to let the bioload catch up before adding more. In freshwater you can get away with it in salt water it can actually throw your system out of wack!
Your probably getting an ammonia spike because your system is trying to catch up with your sudden increase in bioload due to adding too much livestock at once.
I would also invest in a decent skimmer, that is a necessity in this hobby if you want to keep fish!
When adding fish take your time and add one fish and wait a few weeks to let the tank parameters catch up and then add another!