I have been managing/admin/moderating/using forums for a long time now, and they are VERY demanding.
Getting a forum going is a funny process, it can be extremely difficult in more ways than one. One thing I would say is make sure you have some friends you can call on to help you out if it explodes, because trying to run a forum that has ANY form of controvercial content (which is pretty much everythign) is time consuming and often heart breaking.
I have a busy rugby forum, Initially I set it up for around 10 of us to have some place we could go and chat about rugby. It was a completely closed forum with nothing other than the basic front page viewable, and people only got in by invite and approval of everyone else (it was like that after the rugby world cup when the BBC opened up our Welsh rugby message board to all the nations, it was HELL on earth). My forum became known as 'the island'
Anyhow after a year or so I figured that the RWC fever was now past and that we could open the foum up to new members should they wish to join. Word got around quickly, and people joined.
We now have a little under 700,000 posts and during this years 6nations in February, we got over 2.5 million page views.
is it tough to run? Well put it this way, Weekends everyone goes out, gets bladdered, comes home and goes online Half of the members will have watched their teams win, half lose
But I love it, I make no money from it, have no advertising on it, and it eats bandwidth. Worth every penny though!
So to answer your question, decide what you want OUT of a forum before going in, or else it can suck the life out of you.