I take a look at things a bit differently than most people. But let me break down a few things for you how i'm seeing them.
Initial addition of fish: This is where you are most likely going to see an ammonia spike if any. Assuming your tank is well cycled and maintained I would be surprised if you even saw one assuming you handle everything correctly.
The food that goes into a tank is what causes the ammonia production. If you feed x amount and add 3 more fish but keep feeding x amount then you aren't going to see a difference in the ammonia. You're still putting the same amount of food in the tank. With the heavy stocking, you are going to want to feed very sparingly over the next week or 2 slowly amping up the amount of food you feed and checking later on (12ish hours) in the day to see if it had any effect on ammonia. Thankfully for you the nitrifying bacteria is relatively quick to grow.
, the bigger issues will be combating the nitrates that are bound to pop up because denitrifying bacteria won't have colonized enough to cope with the additional load. That and the possible addition of nasties into the tank.