Welcome to the forum
I agree with a lot of what is being said here.
Definitely switch out to sand now before going any further. Since you are new to the hobby, crushed coral (CC) will make it that much harder for you to maintain proper water parameters, specifically nitrate levels, which can be dangerous to corals, and fish if it gets too high. CC will limit what you can keep as far as fish and inverts as well and just overall is really not a good idea. Since there isn't much live rock (LR) in your tank right now and you're just starting, my suggestion is to remove as much water as possible into buckets with the LR and dump out the CC into a container, then, put the LR back in, then sand, then water SLOWLY. I usually add water through a strainer. This will cause less sand to get kicked up and helps to keep the water a little less cloudy. Adding the rock BEFORE the sand is preferred, this gives your rock a more stable foundation. I will tell you from experience, I have done both, so either can be done, but rock first is easier. I, too, think that a sand bed should be 2-3" deep, especially for a beginner. I have found the best calculation to be around 1lb of sand per gallon. If you have a local reef club in your area, you can add bagged live sand such as CaribSea and see if you can get a few cups of live sand from peoples tanks and place that on top of the bagged sand.
You have a test kit, what brand? Are they test strips or test tubes that you must add water and chemicals to?
Once you swap out to sand, add in a raw shrimp and start the cycling process. There are many great threads on this forum and others as to how to properly cycle a tank with raw shrimp and NOT fish, please look into this method, it is much more humane. The idea behind using fish is basically you're placing them in the tank to produce waste. As they produce waste, it turns to ammonia, then nitrite, etc and kick starts the cycling process. The problem with this is that the fish are stuck in ammonia and it burns their gills and 95% of the time, very painfully kills them. Raw shrimp will decay and produce the same ammonia and kick start the cycling process without killing the fish.
If you have any questions about cycling your tank and/or what your readings are/should be, feel free to ask at any time. Many people post pictures of their test kit readings the first few days as they can be tricky to read sometimes.
Since you're cycling your tank, I'd recommend adding more rock now, you can get uncured or "dead" LR. If you wait until after your tank is cycled to add more rock, you'll need to add cured rock, which is usually more expensive.
As for water and salt:
Get yourself RO/DI water, or at the very least RO water. Don't get in the habit of using tap water. You can purchase RO water from most reputable local fish stores (LFS) and some Walmart's carry it as well (not if you live on Long Island). Look into purchasing a RO/DI unit, it will save you money in the long run. I happen to like Coralife's model and Water General's model. Tap water contains many unnecessary and sometimes harmful substances such as copper and chlorine that you don't want to introduce to your tank, especially once it gets more established.
As for salt, everyone has their preferred brand. If you live in an area that has many LFS's, you can shop around for the best salt, best brand, etc. If you live in an area that does not have many stores, stick with a national brand that is easy to find such as Instant Ocean (IO) or IO Reef Crystals.For cycling your tank, go with I), or Reef Crystals, as they are both easy to find, consistent and cheap. I've even seen people using *****'s brand of salt to cycle a tank. Do not cycle a tank with expensive salt, you'll be wasting your money.
Get yourself a refractometer before adding any critters to the tank. The glass hydrometer will work for now, but a refractometer is much, MUCH more accurate.
Don't be too upset that you were given bad information by your LFS, unfortunately good LFS's are hard to find, you're not alone. The best thing you can do is ask questions here and see if there are local reef clubs in your area. Where are you located?
So, can you tell us what equipment you were sold for this tank (filter, heater, lights, etc)?