If you think your BBQ is good enough for catering, theres a low barrier to entry to see if you have what it takes. FOOD TRUCK.
Another option would be to rent a commercial kitchen.
Or, whip up some of our best Que and give it out to strangers with a written questionaire for feedback. Just because you think your food is great, does not mean anyone else does. Dont test on people you know. They will all say its great no matter what they think. Only strangers will be honest.
If you attempted to run an illegal catering business out of your house, odds are high that any competition gets wind of it, they are going to rat you out and youre done. I know I would. Also catering to 100 is not the same as making a rack of ribs on your Big Green Egg in the backyard. Theres an art to it that comes from experience. Its a business built over time and through word of mouth. Part time catering out of your house? How are you going to compete with BBQ restaurants catering full time?? When you get you car fixed, do you take it to a shop thats open every day and has experienced mechanics, or do you take it to some guys house that operates part time out of his garage?