You're cycling a tank, and really, there's no way around ammonia spikes. However, if you're going to use fish, you don't want to use Danios. These fish produce little waste, due to their small size, especially compared to something like Goldfish, which would make the process much easier (they'll spike the ammonia in a hurry). If you must use Danios, I'd start with 7 or 8 of them... they're clearly not a huge concern if you're breaking a tank in with them, so I'm not going to bother pointing out the permanent damage you'll be doing to them. If you instead use Goldfish, get a few of the feeders-- they'll do a "better" job than 7-8 Danios. There is also no need to continue to add fish once the ammonia spikes-- that will simply create a new ammonia spike, which is neither necessary nor helpful. Just stick with as many as you start with. If they die, leave them in the tank-- it will accomplish the same task, which is producing ammonia.
Also, see if the local fish store will give you a handful of gravel from one of their tanks, or better yet, some of the media from one of their mass recirculating filters. Either of these will already be home to loads of nitrifying bacteria, which will expedite the cycle in your tank by essentially giving it a starter culture.
The "inch of fish per gallon" "rule" doesn't apply here, nor does it apply anywhere else. This is a vastly oversimplified concept that is, unfortunately, perpetuated in the hobby. It fails to account for so many variables as to make it silly to consider it, despite the fact that it is frequently suggested.
