sterilizer won't effect the good bacteria in the tank. I have never used one and i don't think they are worth the cost on reef tanks. Invest the money you would have spent on a UV
to buy a small QT tank and it will ensure you don't have problems far better than a UV
As for how long before adding more fish. I would wait until around the 2 month mark to add more fish. Take your time with fish. Especailly in a tank that size because you can't add all that many. Spend some time to research a fish you will really enjoy and then watch for it in stores to find a really nice looking fish. This will also give your tank plenty of time to settle in.
You can keep your self busy by adding some small coral frags since they don't really add much to the biolaod. You will probably be pre-occupied anyway by dealing with the new tank swings. Expect some cyano
, diatom, and algae blooms in the first 6 months or so.