It helps, when you begin, to have a concentric model in your mind of what it is you hope to achieve. Build from the centre out, so that you preserve an appearance of unity and integrity at all points. My first chronology of French theatre listed only popular fairground plays during a 15-year span between 1700 and 1715. In its next incarnation, it will cover all performance arts in France between 1600 and 1800 - and it will no longer be mine, but the combined work of nearly a dozen scholars around the world. The kernel of your project should be something you care about.
Indifference makes for dull work, and enthusiasm enlivens it.
As the project grows, your claim to be an authority in the area will come under ever closer scrutiny. The stronger your claim, the more easily you will attract collaboration. At some stage the survival of your site may depend on the extent to which colleagues recognise it as authoritative. One insight that came to me early in my experiments with hypertext is that it's easier to change the label than to change the content. Call it what it is, and change the label later.