I don't think it's even worth beginning to invite participation for a project like this until you have at least built the minimal mandatory user interface: a map-based interface that at least shows which locations have entries.
Maybe. I'm mostly of the opinion that the map-based user interface is often a bit clumsy and slow, i.e. Wikimapia and can be more of a burden than a blessing.
But they are an essential option for displaying geographic data. You may have an entry for something 6 blocks from me, and how would I ever know about it?