Webspace and money are what you need.
Depending on the package plans for the hosts you're looking at, go for something middle-ground that's in your budget. If you have any questions as to what you'd need, feel free to send an email to the hosts you're looking at: this will also help you get a feel for how their customer service is on the odd chance something were to go wrong, plus it makes it easier for you to set up the forum if you have established a friendly rapport with your provider.
Also, prepare to shell out some cash for decent forum package (like vBulletin, which is what this board is running on). All the free forums suck major ass because they are laden with banners and a generally clunky, low-customizable interface. You might think they're the perfect solution, but if you plan on having a long term type of thing, you'll grow to hate the pop-ups and whatnot.
Don't worry about bandwidth if you're just starting off, just remember to do these two things: put a limit on the size and number of files that can be attached to a post, and disallow remote linking to images hosted on your site. Those two things alone can seriously kill bandwidth: on the site I admin at, before we fixed those problems, we would burn through several gigs of transfer a day because people were uploading images to our server, and then using them on other high-traffic boards.
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