I have used Seachem's Prime for a dechlorinator for years (started with reef aquariums 20+ years ago). It has the ability to bind ammonia (and nitrite if you 'overdose' it per the instuctions, read carefully). The ammonia will still show up on the test kits (sinces its really still there, just held in a state that is safer for fish). If you want to save some time and effort on water changes at the beginning, you may want to look at getting the Ammonia Alert disk they sell (PetSmart had them for $5.99 last I saw). It does not react to the 'safer' ammonia that is bound, so you can know 24/7 if there is ammonia you need to worry about. If it shows an unsafe level, you can use Prime to bind it (binding only lasts a few days) or do water changes to bring it down.
I'd start testing for nitrite once you see some ammonia registering. How often to do water changes depends a lot on the bioload of your aquarium (which is light for the tank size, so good), and the amount of food being fed. Remove any uneaten food promptly so it doesn't decay. Your test kit will guide you on how often and how much water to change.