I would get the basics done first before asking people to join you, (domain, software, style, general layout, direction you want to go) a few reasons:
You will always be the ultimate boss or owner having started it, you get the first and last say at all times... this also reduces disputes at the start in what direction to go... (e.g. people will argue about forums styling for days.....)
Lots of people wouldn't understand your vision, or have a slightly different one, so best you start without them and that makes it easier to sell your own vision to others.
You can bring people on board as needed with skills that suit what you need for the forum - eg you might not need 5 people who all like the same topic but zero experience in running a website, but you might need someone that is a really experienced Forum Mod for example.
Having multiple people at the start can be good for costs, but then that can create issues later down the track when people wont pay up or feel they have a owners stake in the website because they contributed when it started - better method again is to do it yourself and ask admin team if they might donate to help cover costs at no obligation.
edit: remember the saying "too many cooks in the kitchen"