First off, before you get anything, figure out what you want to keep in the tank. This need not list every piece of livestock you want, but it should be something that gives you a general idea of where you want to take the system.
I would also say that your better off with a smaller system that's a real gem rather than a second rate larger system. I also recommend buying top quality equipment. This doesn't necessarily mean most expensive, but you do want something that will last and you only want to buy it once.
Figure out what you need to get the system running verses what you would like to have. For example, you will need some sort of filtration and most likely skimming, but you don't need every possible reactor and other addons. the can come later, if you need them.