truthfully to do a fish only you dont really need much. If you want basic basic, alls you need is water, salt, some sort of filtration ( some use hob penguin type, some use canisters, and some just have skimmers) and fish, and maybe some sand. Live rock isnt needed, although it is a good natural source of filtration. Skimmer isnt needed if you do your water changes weekly.....I didnt have a skimmer on my tank for quite some time, and it was a reef tank too, but once you go reef its a nice added extra to have a good skimmer. Lighting is another thing you can get away with just the basic.....but you need to keep in mind that if you do want reef, you might want to just buy a good light rig and be done with it. It really all depends on how in depth you want to go with it. Befor you jump into anything, I'ld recommend reading up on starting a sw tank, and a reef tank, so you can get the full idea of what youre going to need...that helps so you dont have to rebuy/upgrade things later down the line. Dont forget to ask as many questions as you'ld like, were all happy to help!