If you are deeply attached to the BBQ idea, you can reduce costs some by hiring in the pig roasters and doing some of the set up and sides yourself.

First an idea of the project:

You are talking about around 500 pounds of prepped food, not counting desserts and beverages.

Day of, requires 240 pounds of whole hog (which is usually 2-3 carcasses) to get around 120 pounds of meat; 4 people just to handle the pits/spits. They will not be at the wedding, they will be setting up.

20 gallons mac and cheese, 10 gallons slaw, 4 gallons pickles, 20 pounds sliced onions, 7 gallons sauce plus sauce for the tables, 50 pounds bread and rolls, 12 pounds butter, 12 gallons baked beans (16#10 cans), 80 pounds each corn and green beans (16#10 cans each)

To serve 300 people, 4-5 people in the kitchen and 15-18 out front, to set up, serve, and clean up the party; they will not be at the wedding, they will be setting up. Definitely requires a fully equipped large commercial kitchen.

That is assuming that all possible prep is done before the day; about 8 days work, counting the shopping and the cooking.

I never recommend more than 120 at a self catered wedding for an inexperienced crew, and even that is pushing it. Please go read the wedding dinner article and think some more about your plan.

Then write back.