Regarding network effect... I actually have that problem solved. 12 months ago, I coauthored a book called Software Engineer's Guide to Freelance Consulting which has been a bestseller on the Amazon marketplace. I started cultivating a Slack channel of developers. My next step was to write scrapers/crawlers of ~50 freelance programming job boards in order to keep the developers in the channel happy. And I have also tested advertising campaigns, and they're successful in attracting developers to sign up and complete their profiles. So if we need to scale the developer side of the market, that's a solved problem for now.

But I just haven't found the acquisition channel for the people who post the tasks. Perhaps I should focus on marketing to developers rather than middle managers..