Hi Ed:
Are we talking about a tank you're going to establish, a newly-established and still cycling tank.. or an established tank?
Ammonia and Nitrites will/should only be a problem with new and cycling tanks. If you're just setting up a tank, test kits for these are good to have (and, by the way, I recommend cycling a tank without fish). If you have detectable ammonia or nitrites in an established tank, it's a sign that something's wrong with your biological filtration.
If "Water change or not?" is a question about whether or not you need to perform water changes.. yes, you do.
Testing the pH of your tap water (do it twice: once straight out of the tap, once after letting the water sit for 24 hours) is a good idea, since different fish come from different areas, they have different water requirements and it's a good idea to keep fish that are a match for your water.
Aimee