For a first foray into business, I'd recommend against building something that requires network effects.
http://en.wikipedia.org/wiki/Network_effect
For every Facebook or Yelp, there's hundreds of network-effects-based sites that never gain any steam, and they don't see anything from it. Also, what you're talking about is notoriously hard to get money out of.
For a first business, sell something to people. Take Hacker News' own Patrick McKenzie* (patio11) - he sells Bingo Card Creating Software. His blog is here: http://www.kalzumeus.com/
He sells things to people. If he tries something, he knows right away if it's working - he gets bingo card sales. If no one bought his bingo cards, he would know it's not working and he'd have closed his site. You learn a lot about business by selling things to people, and it's got the most clear and insightful feedback.