I've been working in the Media Production for 6+ years, and i'm good at shooting (producing) commercial video. Now I find my interest and love in the commercial and creative field, and want start my own creative agency.
Hi, first let me give you a big applause for wanting to start something, it is not easy and requires guts.
In my experience you should first know what you are good at and what's your passion, if you passion lies in just producing, then start by hiring someone who makes sells. Still I would definitely recommend you to learn how to sell and just go out there and do it.
Don't make the mistake of trying to have everything perfect, all the tools, all the employees, the offices, just go out there start and finish, sell your services and deliver the best result.
From that point forward and once you find yourself in business then think about the structure of the agency.
Keep things simple:
1. Come up with the core product / service
2. Create a system to sell it and deliver the result
3. Once it is running smoothly, make changes and evolve your core.
My best wishes in this adventure