Trading outrights and trading spreads are two different animals. Trading outrights is simple but very difficult to be consistent picking direction correctly. Trading spreads is more complex for the very reasons illustrated by the posts in this thread ... how to select the markets, determine weightings, ratio, etc. And you have the additional transaction costs. If you have an edge in trading the relationship of two markets, then it may be worthwhile to tackle the complexity of spread trading.
Thanks for the input guys. I mean I didnt start trading yesterday. Been doing it for over 4 years. Trading outright isn't as easy as you've described it to me lol. It's hard to pick the direction. Just try to test this out, after all mostly all hedge funds and big banks do it.