It was set up and running with established love rock from a friend of the family's tank for about 2 weeks before I added fish. I only added the shrimp 3 days ago.
Thats was fast.
I don't know that your tank was fully cycled when you added fish. If it was, then adding all of that livestock at the same time created the ammonia spike as the bio load was greater than the existing nitrifying bacteria colony could process.
I would agree with your choice to do a water change. Do 20% of the total tank volume every other day and test for ammonia on the days you aren't doing the water change. After that, weekly 20% water changes for nutrient export and element replenishment for maintenance.