Thoughts from listening to Roman Mars of 99% Invisible in today's webinar "The Challenge of Visualizing Sound":
A key difference between the "pros" and solo hobbyists like myself is that the pros divide responsibility among several team members. Roman says he doesn't write comprehensive scripts with "cogent sentences;" he cobbles ideas together and hands them off to another team member to clean up. He is also able to pay producers for many of his stories.
Promotion: Roman says "I've exclusively relied on word of mouth." However, having a radio background, he also had access to a very high-quality network of first-circle listeners. Milestones included being picked up by Jesse Thorn, BoingBoing, and Radiolab.