My understanding of forums are that you need a huge amount of up front traffic that most people fall hopelessly short of. For those who have forums: Once it is established, does it by and large run on autopilot? Obviously you would have to ensure you always have several moderators around.
I don't run a forum but I know several individuals that run fairly successful ones. Technical problems can arise such as database errors, server failure etc which would require your attention otherwise you could very easily lose users.
As long as you have a solid userbase, that checks in often, as well as new users joining, asking questions, etc, a forum can honestly run itself.. With a little push and effort, it can work out great. But as you said, the up-front traffic is hard to get. Sometimes it's best to pay a few people to sign up and make posts on the forums. No one likes to see a completely empty forum.
Forum's scope is the most important factor. If you choose the right topic on the right market, you require less effort to success.
Heed Cabron's advice. If you don't want to moderate it yourself, find a forum member who is useful and see if they want to do it for fun. Many forum users enjoy a little free "power".
You definitely need mods and admins to make sure things dont become hectic on the forums, but you can probably get your members to do that.
Forums needs to be monitored all the time to avoid saturation by spammers... and you need mods (either free or paid)
i admin one forum and mod another one, both music related and both take quite a bit of time. once you have things setup and can get a few mods then you should be pretty sweet.
I think a forum that has an active and visible administrator, that posts frequently, is more attractive than one that doesnt. Administrators on big forums tend to find themselves as the social heart of the forum, and posts by admins tend to generate a lot more replies as well, which will make your forum seem more active and social....thats been my experience.