Happy to answer any questions anyone has about bootstrapping, running a marketplace, trying and failing to raise money, etc.!
I honestly don't remember my success rate as it's been a long while, but I want to say it was at least 25%. Keep in mind I was pitching a free product that vendors are already used to (there are TONS of wedding vendor directories.)
As for scaling, no idea. Some CRMs allow you to mass-send email but I worry about those - feels scummy, though maybe I should just get over that feeling and try it out.
Good luck!