By the sounds of it you're new to photography, or at least SLRs (and I'll assume lighting). I'm not going to say you can't produce great quality portraits, but give photographers some credit... it takes more than just a nice camera to take a great portrait.
If you've never done off-camera lighting before, then you're not going to get that figured out in time for these photos. So if you're using available light you're at the mercy of the sun, which is much less flexible. I would research "natural light photography", there's a ton of info on it. And I'd buy a Canon 50mm 1.8 lens (assuming you only have the kit lens). Then I'd shoot, shoot, shoot as much as I could to start figuring things out.
Or, I'd just pay a professional that knows what he's doing.
