Hello I'm very new to the saltwater aquarium world

Hello I'm new to the hobby. I have a 20g tank. I am going to be making a salt water tank. My first thought was to get a mantis shrimp but after doing tons of research I have decided right now it's not for me. I would like to have a predator tank. I would like to do some coral as well I like candy cane and birds nest I know those are low light corals but I am also interested in the more exotic corals that require high light. So my question is what are other awesome predator fish you would suggest for a 20g tank. I will get the lighting after I figure out what kind of predator I want. Any ideas would be much appreciated thank you.