New tank/ suggestions/ coral?

Hey, im new to the saltwater reef aquarium and need some advice. I have a basic 20G aqueon tank with about 13 lbs of live rock and 1 inch thick live sand across the entire tank. I used the stock heater that came with the tank and swapped the filter out for a stock filter that would come on the 50g aqueon tank. The tank has been up and running for about 3 months now and all my salinity, nitrates and nitrite levels have been fine. I have a clean-up crew that consists of 3 red leg hermits and 2 blues, with 2 bumblebee snails and a lawnmower Blenny. I decided to go with a Fluval 25W 250000k LED system. Seemed pretty basic for a beginners tank. I have already gone through the diatom algae stage and now I have white Copeopods inside the tank. I want to start with some corals but not sure what to start with. Am i ready for a few frags or do I need to do something else in preparation <<