I guess if you can cook for 900 people, you are pretty much in business already, just start charging
I am a private chef in my day job, and barbecue is just an ad on for my company and a hobby for me! it's fun! I did pulled pork for 470 people in September and it went well... it was my first real big event. I cook for 36 hour straight, slept in the car:)
great money, but loads of works especially for my first time I learned so much!