Setting up a new website is a process of many tiny steps one has to take and setting up a succesful new site has even more obstacles.
My philosophy was always (since I put my first website online in 1995) to go online as fast as possible and to tweak the site while being online – based on the REAL WORLD feedback of my users. True is, that you have to have the right idea first, no doubt. But even with the brightest idea you still need the feedback of your users to get it right over time.
Many of the webmasters I know what to make the big hit at one fell swoop and work months on the features they think would attract many new users. Well that could work, but will most likely not.
The best “philosophical” approach for me in the past was always to create a solid skeleton of a site, with the basic ideas laid out and working fine and then, each week, rolling out new features, which were requested by users. That brings you happy customers, because they get what they requested and you will have a site, which REALLY covers the market needs.