Um, will consumers buy it? Thats a problem you need to ask about. Didn't you say your target audeience is going to be there? Thats what market research is about, standing in front of someone and asking them, "would you buy this?" Usually, people are nice and say yes, so you always have to discount that, but if they say no, then you really need to start thinking about your business.
Ask people how much they would pay for it, what they think of the idea, get any suggestions, ask people what other problems they have. Ask publishers if they are interested in your idea. Don't treat the publishers like consumers. Treat them like businees contacts, because they will be. Network among the publishers, ask them if they would be interested in hearing from you when you get your site up, and get their bsuiness card (Purposely ask for it, they'll all have one). Write down on the back who they are and what you talked to them about, cause in a few months you'll totally have forgotten.
When you're talking to gamers, and if they seem interested, ask them if they would want to sign up to be notified when your site goes live or if they want to be a beta tester, that sort of thing. Don't send them emails before then, and let them know this. Just have a clipboard with a piece of paper on it. I wouldn't ask consumers for a business card, thats kind of awkward, like you might actually call them. It helps not to be pushy, so if people show a real interest, you can always email them. Accept a card if they give it to you.
I wouldn't worry about a placeholder site or business cards, although they are cheap. If you don't have a site yet, its not like too many people are going to be seeking you out. You need their cards. If someone wants your contact info, you can always ask for their card and send them an email that night, or write it on the back of theirs. I mean, cards are cheap, but it won't kill you not to have them.