The first three points in this startup checklist basically require you to do adequate research into your market. You have to know what the value of your offering is to the people you are offering it to. For example, there's no point in pricing your premium content at $3 a posting when the exact same content is being given away at a larger, more established site.
The barrier to entry into the online market is much lower than traditional businesses, which is great. But, it's a double edge sword because the easier it is to do something, the more people try it out. This means that you have to work harder at distinguishing yourself from the melee of other startups out there - because, believe me, there are a lot.