I think that 98% of the time, the right answer is to start out and remain focused on one vertical until you take it over. Most startups expand far too early and then fade out everywhere (this is often the fault of bad advice from investors). Facebook started in an extremely small vertical (Harvard undergrads), then expanded to a still-small vertical (US colleges), and then at some point took over the Internet.
Why did you pick this vertical to start with? It seems there are a lot of services helping people get restaurant reservations. The idea of breaking down tasks into small action items and farming them out to people seems good, but this doesn't seem like the most pressing need. What else did you consider as a first vertical?
How many users do you have, how much do they pay you (and how much do you pay the agents per task), and how fast are you growing?