Here's what I would do. Find and vet one good specialist. Perhaps for just one of the platforms. Have them at the ready and tell they they'll be paid per job. Validation comes when someone hands over their money for your service. I'd then share and promote the service everywhere I could. I would do it founding members style... meaning, I would promote that I'm launching a new service and looking for a few founding customers to help me shape this into the perfect service for them. In return they'll get a deeply discounted founders rate, which will stick with them for x amount of time. If you get a few buyers, you have validated the service. You connect the buyers with your specialist manually and off you go. Don't need a website for any of that!