Ok. You don't need coral for a tank. To start a SW
tank, you require sand and live rock for your bacteria to grow on. You want 1-1.5 lbs of rock and ~1 lbs sand per gallon. This is where the bacteria will grow and prevent ammonia spikes from killing your livestock.
I will not discuss your want of livestock as I have no experience with them. All I know is that rays need a special fine sand so they don't cut themselves. I believe sharks and rays will need more than 200 gallons...but unsure. Check out liveaquaria.com and that will give you the min requirements for such livestock.