i don't think a 6g tank would be a wise move for a first time sw person. a protein skimmer for a 6g tank would be overkill, especially if you have a ehiem liberty filter working. using a heater is wise only if you can't keep your water between 72 and 78 degrees, the ideal temps. for most marine fish. live rock is a term used to describe a rock from the ocean teaming with all sorts of differing life on there, anything from algae to inverts. live sand means the same thing, but with beneficial bacteria and organisms in the sand. cured live rock refers to the state of live rock where it is suitable for aquarium usage, assuming you are not cycling your tank with live rock. cured live rock means normally removing all unwanted organisms that would be detrimental to the tank's livestock BEFORE putting it in your tank, a process which can take a few weeks. an over-the-back filter is perfectly fine for a smaller sw tank in my opinion. i have no idea what a calcium reactor is, but my guess would be a reactor that produces useable calcium for a tank. my suggestion to you is to read up A LOT on saltwater tanks. is this your first tank ever, or are you just starting in saltwater? good luck with the tank. my advice is to cycle the tank properly, and be patient! you will be rewarded in the end.