Beginner Predator tank

Hey guys, I'm new to the tank world. Lately I've been reading anything and everything about setting up a salt water tank. I've been very interested in a FWLR Predator tank but there is so many conflicting information. I already have a 55g tank previously used by my grandparents as a fresh water tank. The main fish I am very interested in is: Snow flake eel, Dwarf lion fish, Niger Trigger, and maybe a angler fish in the future. What are some basic needs and steps to start it all out? I have a friend willing to give me his live rock and sand, as well as water from his salt water aquarium. Any input and recommendations would be appreciated. Thanks!