good place for additives is BulkReefSupply.com
as far as lighting. you really need to figure out where you want this tank to have softies, SPS, etc..... If you eventually want to go SPS then you need to buy the best light now. If you buy a light that will only work on softies and you spend $400 and then decide you want to keep SPS and you will. You will need to upgrade the fixture and spend say $700-$1500 So its best to go ahead and spend the money and get the right light first. Its up to you wether to get LED's, Metal Halid or HO T5's. When it comes to skimmers, and lighting you get what you pay for they are the most expensive and most important pieces of equipment. LED's look into AI Sol or Vega, EcoTechs, Metal Halide I have no exp. with, T5's look into ATI fixtures