The main resource you need is time.
If you don't have time to post at least 25 posts per day on top of your usual website activities then you should not start a forum.
In the first few months of owning a forum you should at least do 50 posts per day.
One of my more successful forums (which I have sold now), I did do around 50 posts per day and within the first week there were two members with >100 posts and about a dozen other members contributing on a daily basis.
Ask Will again for more info ;)
But if you are not prepared to commit like Will has forget, he works around the clock and he also is very savvy, which means that what he does he sure tries to get more things right than wrong, and his experience is a solid advantage
So you need effort and knowhow and that is just for starters :)
IMO the time must be the limitation for Will.
And emotional energy, lots of emotional energy. Building communities is a labor of love. If you don't have a serious, deep, and enduring love for online communities your failure is going to be very painful.
Favors is another huge one. I've spent years building relationships and taking care of people -- and I've called in more favors for this project than for every other project I've ever done.
Money helps, of course. Software, hosting, and promotion all cost hard money.
Time for sure, lots of ideas, and perseverance.
If you don't have the time you can't do the crime :D Erm make the forum succeed.
The main resources you need is people. The right people willing to spend the time to help launch the forum. Once the ball is rolling, you need the right people to keep things rolling and under control.
I do not put too much value on design and tech related plusses unless of course the forum is tech related.
i would say..
1) Time you willing to spent in the forum
2) A good team of forum moderators and admins
3) A group of members that is always willing to contribute good quality post. Always, people like to take more than they give.
4) At least some backups funds for the community. E.g. organize contest, give free gifts etc.
5) You need to have something different, maybe in terms of technology, ideas, or what. because nowadays, forums are getting more and more. You can find it anywhere, so what differentiate your forum from others? why should i join yours instead of others?