10 gallon fish tank question?

I recently decided to set-up an aquarium using my brother's 10 gallon tank. I cleaned the gravel/substrate as well as the aquarium objects. I researched about "new tank syndrome" and a good way to set-up a healthy tank. However, at the pet store, I impulsively purchased two cardinal tetras instead of zebrafish (I also purchased a black mystery snail and a live plant: I forget the official name but I can provide that later). I checked the water temperature, the pH, nitrite, ammonia levels: they are all suitable for the fish. Nonetheless, I am concerned that the fish will not be healthy since they are in a group of less than 5. Also, I eventually want to add bottomfeeders and potentially zebrafish, but I obviously can't put more than 9-10 small fish in this tank. How would you suggest going about the next 6-8 weeks to establish a good nitrogen cycle? Any other suggestions or warnings?