It sounds like you're getting a lot of good advice on the fish, so I'll stick to the cycle...
There's an article in the sticky's about doing a fishy cycle. you should check it out if you haven't already. The basics go like this:
Your amonia will spike, the bacteria will grow to compensate, the amonia reading will go back down. This process will repeat for nitrites. Then you should see a nitrate build up. Once the amonia and nitrites are reading 0 consistently, and your nitrates are rising your tank is fully cycled.
Keep in mind since there is life in your tank, any ammonia or nitrite is toxic to the fish. You want to do water changes to keep these levels as low as possible. Twice per day if necessary. If either number gets to .5, do a large water change immediately. I hate to be a pessimist, but there's a good chance that the tetras won't make it through the cycle no matter how good of a job you do. I can tell you from experience that a properly managed cycle can be done without losing fish. But a lot of work has to go into it.
Congrats on doing such a great job!!!