Almost any commercially available fixture for aquariums will do the job. Some better than others. Zoas are pretty forgiving and don't need as much light as lps or sps, so you don't need MH. If you want inexpensive, a good t5 fixture will due. If you want more control of power/intensity and color, an inexpensive led fixture with dimmers will do just fine. They can be had for under $100 on Ebay or Amazon. Do you understand why your corals need good light? Do you understand that they prefer blue spectrum to be healthy and grow? I'm just asking to find out how what you know. I was years into the hobby before I understood half of what I would have been useful to know when I started.
And not being in a hurry is the smartest think you said and the best thing you can do. Asking question is 2nd on the list of good things!
But it sounds to me like you may have other issues to take care of first?
1) Your nitrates are too high. Has your tank finished it's cycle?
2) Test strips? They can work... but I'd really like to hear that you plan to get better test kits. It will be a simple tank and easy corals so inexpensive API kits for ammonia and nitrate along with a hydrometer for testing salinity (specific gravity). Later you'll want a kit for alk.
3) Using RO/DI water is great. Are you making it yourself? Purified spring water... not so much. If you have to buy water at the grocery store, use distilled water.
4) Are you doing water changes? With a small system and easy corals like zoas, you can avoid a lot of other hassles by doing regular water changes.
