Some tips from my own experience administering forums:
1. As someone said, pick your moderators carefully. You should know the person you appoint as a moderator well and should be on the same page with them regarding what needs moderated, and you should get along with them quite well. That doesn't mean confine your moderators only to friends etc, just make sure your moderators are trustworthy people. The main point though: don't ever have too many moderators, especially when the forum is young; it makes for a weird community. If you have 20 active community members and 5 moderators, something's not right! From my own experience, if you're putting as much into running the forum as you should be, your own moderation efforts should be plenty until the forum has at least a couple thousand posts. Then consider a moderator or two.
2. Perhaps it's bit late for me to say this, but vB is completely unnecessary for a forum; try some free systems like SMF, PHPBB, or FluxBB before deciding to buy vB, you might find something you like just as much for free.
3. Just because your forum is there doesn't mean they will come; it isn't a retail storefront in a shopping mall. Unless you put something into it, don't expect anything of the forum.