This is one of the places where fishless cycling or bio-spira can be really helpful. I fishless cycled my 50 gallon and added 14 cichlids at once, I never had any sort of ammonia spike.
I was adding 5 drops of ammonia a day, way more than any amount of fish would have been producing. When I put the fish in the amount of ammonia available to the bacteria colony dropped, so to them it was as if I had lessened the bio-load. It is much easier for the bacterial colony to adjust downward
If you do want to add more fish later, you can move all the rocks around, this messes up all the boundaries the fish have set, and they have to work them all out again, giving the new fish a chance to claim some as well.