Asking what the the size of your stop should be without knowing how you are trading is meaningless. The right answer might be one or twenty. Regardless of what else you so, I would suggest that you spend some time trading with auditrack, or something similar before moving into real money. You may want to reconsider the vehicle you suggest, as it moves pretty quickly and is a little squirrilly for somebody just starting out. One last thing, the best advice I have seen given to new traders, and you have heard it here too, is to start with one-lots. Even on the floor, where you can get in and out with relative ease, most new traders start with one-lots for a while (sometimes weeks or months) until they are consistently profitable. Many are 5-lot traders for years afterward, making 6 figures doing it, and never get bigger than that. The others who started too big are gone. You have nothing to lose initially by trading too small, and you WILL lose money getting started. We all wish this business was as easy as a lot of people would have you believe. All that said, if you can stick around for a couple of years, you will probably make it, and it's a good life once you do!
Good Luck!
Jessie