We are thinking monthly fee. Your point on charging to search devs is exactly what we are going for. People won't sign up unless they are serious about building a project.
I agree with this. A monthly fee only makes sense if I have an ongoing and steady need, but the presumption is that this is project work. Your charge needs to be project-based.
Agreed. A monthly fee doesn't really make sense. If it takes any more than a month to find a dev, there's something wrong with your system. That means the most you'll ever make is 1 month worth of fees. Charge a flat fee...but wait until I find my tech cofounder:)
The problem with that is that you want to let them communicate freely to strike a deal, emailing each other details etc. Then they can just negotiate off-site and you're cut out.