Forums are extremely hard to get started when they don't have any specific website building them out first. You will need one heck of an interesting topic, or buy out a current forum and migrate the users over. As for profit/revenue, premium member perks, adsense/words, donations? One other thing people overlook, but is relatively sleazy, is selling their information. However make sure it's clearly defined in your TOS.
Making forum is a good idea but you need to invest $300usd+ for advertising and promotions inorder to make it successfull. Then think on income from it.
Almost true. My forum, i didnt invested anything i was earning 300 USD monthly income. But i was giving excellent programs. But well. Then, the hosting dissapeared (hophosting.net) i used to manage dns on that hosting also, and well, program become outdated, etc. So here i am.. Thinking if i create a forum or no. If yes what would be the subject.