So far you have gotten some great advice. The largest gig I help out with is around 250 people, 25% of which are kids. It is a freebie (no charge) put on by a broker friend of mine for clients and family, so I don't have a clue about money and profits, etc. I think this is the 10th or 11th year, here is what I have learned. Just my $.02 as we are still learnin'
The tables are set up so the serving line is on one side only. We use small and medium plates and small bowls. This makes the line move faster and controls portions & waste. Big eaters can just take two plates or make a second trip.
Sides are the first thing in the serving line. Chips, beans, tater salad & coleslaw. A selection of buns and white Texas Toast is next.
After that we have "kids food" as in a roaster of sloppy joe style ground beef and a warming roaster with grilled hot dogs. Easy, and the kids love them. Usually the little kids bail out of the line at this point.
Then we have chicken, but only drumsticks, because they are easy to cook, they stay moist in the holding tray and they have a built in handle.
Then we have a table where 2 of us are giving samples, slicing meats to order or dishing up the pulled pork for either a plate or a sandwich. A minimum of two sauces are in squeeze bottles. This table is right in front of the smoker, so we can rotate products and keep things warm. What it really does is give us time to show off a little while explaining the lo-n-slo cooking process, the wood flavor, the various meats and sauces. It gives people the warm fuzzy feeling and makes them feel special. We also remind them that we have some go-boxes if there are any leftovers. We mix drinks or have our beer in insulated mugs, so we're not openly drinking in front of the guests. We use those disposable food serving gloves and we keep the cutting boards spotless.
Sweets like cookies or brownies are at the end.
Coolers of beer and soft drinks are the last thing in line.
Garbage barrels are everywhere.
Good luck on your Barbecue!