Welcome to AA!
For the filter, most people use live rock as biological filtration. Good place to start is 1-1.5lbs per gallon, and you can add more from there. But, yeah you could use your filter too, but they tend to become nitrate factories when not cleaned routinely. As for sand, go with dry aragonite, about 1-2lbs per gallon. As for skimmers, I would go with either a CPR Aquatics or Reef Octopus skimmer. I highly recommend Hydor Koralias for powerheads, two K2's or two K2's should work. I would start with Instant Ocean for salt. Get a refractometer as they are a lot more accurate than hydrometers. Depending on if you are going to make it a reef or not, the Nova Extreme Pro 6x54w T5 HO
fixture from Current USA would allow you to keep anything, if not going reef, any old aquarium light would work. Grab a liquid test kit. Get two heaters in case one fails, or grab an extra one if you already have one from when you had it set up as a freshy. Get a thermometer if you don't have one already. Errr....think that covers it all?