It's kind of funny to me to hear the words "portfolio" and "investment" when talking about futures. Some may disagree perhaps. But just ignore the percentage that you have to put up because it might as well be zero because it's so low; pretend it's free. All you are doing is agreeing to lose (or make) $x.xx per point that it moves. Those are the dollars that matter. Percentage of portfolio doesn't really have meaning here, to me.
As for the intention, well that's just the thing: You have to have an intention first,, because these are tools, a means to an end, obviously not things you just buy and hope they increase in value over time. This intention is either a hedge or a wager (disregarding spreads for simplicity). The futures price and underlying will converge as time approaches expiration so if the futures price was above the underlying when you bought it then your "investment" is losing money every day that you hold it. And conversely if the futures price was lower then you may make a modest amount just from the passage of time as they converge. That underlying better do what you wanted it to.
I don't know. These things are not instruments that you just buy because the underlying "seems like a good thing to invest in". And I think I'm hearing a little of that here. It's just two guys betting against each other; it's not an investment. It's fine (maybe even desirable) to be on the losing side of the bet when it was a hedge, or you're offsetting another position that went south (or could go south after hours, like an option), locking in a price if you're a farmer, etc. But not for random investing without a pretty specific goal in mind, a specific thought about what the underlying's going to do (and when) or at least about what people think it's going to do. Market expectations are already built into the price; no free lunch on Wall St.
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