A few tips...
1. Get a good book and read, read, read... "The Conscientious Marine Aquarist" by Robert Fenner
2. Surf this site and read as many posts as you can. Can't tell you how much that helped me when I was planning my system. (Hmmm... guess I CAN tell you, because I just did!)
3. Don't assume what you know from freshwater carries over to saltwater. Stocking levels are normally lower with saltwater, freshwater ich is not the same as saltwater ich... you get the idea.