Welcome to the addiction Bill. First thing I would do is to replace the 500watt heater with a 100 watt heater. Reason being, if it ever goes bad, which it will eventually, it will fry your fish VERY FAST. A 500 watt heater is a massive overkill for a 30 gallon tank. Generally 2-3 watts per gallon is the recommended size. Some even get 2 heaters (say 2 50 watters) to avoid the possibility of failure even more.
30 gallon is a good size to start. The going saying is "as big a tank as you can afford". Bigger the volume of water, the more room for error and additional stability for the creatures you keep. Stability is important. Salt in a fish only tank is not all that important when it comes to brand. I use Instant Ocean. Works fine. Tap water is "ok" for fish, depending on what you have in it, but it is VERY important to use some sort of dechlorinator like Prime to remove chloramines from it.
The important thing is to go slow. Mix the saltwater to give you a salinity of about 1.025 measured with a hydrometer. The big floating glass hydrometers are good and affordable. The swing arm styles are a bit less accurate and tend to become moreso over time.
Temperature wise 75-79 degrees is where you want to be and I would opt for sand and live rock (or base rock if cost is a factor) over crushed coral or gravel. 1-3 inches of sand on the bottom of the tank is good and if you are not using a protein skimmer, it is important to do bi weekly water changes around 20% of the total volume of the tank. I am a big fan of running carbon in the filter as well.
It is crucial to GO SLOW when it comes to adding fish. The tank needs to cycle in order to establish beneficial bacteria that can process the fish waste into unharmful nitrate from ammonia. Think of the fish as living in a toilet. The cycling process takes about 4-6 weeks. I don't advocate this, but many cycle the tank with A damsel to get the process going. I like to use a decaying frozen shrimp to start it.
A 30 gallon tank can generally hold 3-5 smaller fish. Clownfish, pygmy angels, cardinals, grammas, and damsels are some of the types that work well in a small tank.
Hope this helps. Good luck.
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