This is for suggestion only. Use the rock you have and more dry rock for the reef base and then add another thirty or so pounds of fresh live rock. Florida live rock is four or five dollars a pound and you'll get plants, corals, sponges, clams, and sometimes mitrax crabs, urchins, nudibrancs, snails. Occasionally a bad hitchhiker but rarely and at the stage of your tank you can remove anything you don't want. Many people who are serious about the corals they raise are adamant about not using live rock but personally I like the many types of life that comes on the fresh rock. I get mine air freight overnite and most of the life survives with little or no die off. A 55 gallon tank has some layout problems due to the 12" from front to back. The dreaded wall of rock probably is the best option for that tank unless you want a larger open area for fish. The fresh rock will seed the dry rock with the bacteria and all you have to do is add an ammonia source (fish food will work) to keep the bacteria fed. Lighting and water flow are critical for a reef tank. Lots of information here and on many other sites. They say measure twice then cut once. The same is true of a marine tank. Lots of research before you jump in so you avoid mistakes that take the fun out of the hobby.