No problem, I am by no means an expert but I am always willing to help. I guess we'll start from the bottom up, literally. Is their room for a sump or wet dry filter in the stand under your tank? A canister filter in saltwater is a nightmare, I used one for a year and a half, I know. Your can get an overflow that hangs over the back if needed, I don't know if your tank is drilled or not. A skimmer is optimal but not absolutely necessary for a fish only setup. You need to keep the water in the high 70's. I don't know where you live, but in Florida heaters are not a must, my tank stays 77-78 on its own. If that isn't the case for you then you will need a heater.
There are several things you can use for substrate, most people go with sand. You can buy sand at pet stores, there are many types to choose from, its all personal preference. Aragonite sand is common, I have white sand. Some animals can't burrow in course sands, you will have to research the fish that interest you and see if that will restrict you at all. I wouldn't use crushed coral, if you decide to go with sand you will need to rinse it thoroughly, Google and I'm sure there will be several methods listed. I would buy enough for a 2-3 inch thick bed. In your tank 30-40 lbs should be plenty.
Now onto water, you can either purchase RO
water from your lfs
and buy salt and mix accordingly, or just buy the water premixed. RO
water is purified for use in aquariums, you can purchase an RO
setup but they are expensive. To measure the salinity or specific gravity of the water you need a refractometer. Hydrometers are inaccurate. The salinity required will depend on what you want to keep, usually for fish 1.021-1.024 is ideal, some corals need slightly higher.
When you add the water, put a trash bag over your sand, then a pie pan over that, pour the water on the pie pan, this will keep your sand from stirring up. Once things settle down add your rock, dimensions really don't matter, you want porous rock so you have more surface area for bacteria to grow. Try to get atleast a few pieces of cured live rock to seed the tank. You will need 35-70lbs total.
Lights all depend on livestock, if you want corals and anemones you will need high output t5 or led
. Metal halide and power compact lights can cause water temperature issues in smaller tanks. For fish only a high efficiency t5 strip is both affordable and sufficient.
Once everything is set up throw in a raw shrimp and the cycle should begin. You will need a liquid test kit to monitor levels. Test strips are very inaccurate. You will need a Ph of 7.8-8.2 and no ammonia or nitrite for the tank to be safe. Nitrate should be kept as low as possible by doing water changes once the tank is done cycling and you begin to stock it. You should see ammonia levels to start the cycle, then nitrite and finally nitrate possibly. Do not add livestock until the ammonia and nitrite are zero. Let me know if you have more questions, I will help as much as I can.