I'm not a caterer, so take that with a grain of salt... and maybe your customer won't be open to my suggestions but once a year I'm one of the cooks at a business event where we serve 200+ people (I think this will be our 20th year) there are all ages of adults and kids too. We buy the nice Ballpark all beef franks and cook them in roasters with beer, then move them into foil hotel pans and put them in a 250° smoker. This adds a layer of flavor but turns the dogs a deeper color. They are returned to a roaster with some liquid, but we mist them occasionally with a weak beef broth. Some people don't even want a bun because they are so good plain. And we have a bag of corn dog sticks for some of the little kids that want to go that way. We have all the standard condiments like mustard, ketchup, relish, chopped onion, couple kinds of peppers etc.
Instead of burgers and the hassles associated with them.... we make sloppy Joes with more of an adult recipe, not the grade school cafeteria style of sloppy Joes with the steamed meat. My recipe calls for chili powder, black pepper, red pepper, garlic, onion, celery, green peppers and seasonings. The meat is roasted in pans with the dry ingredients on top, then incorporated before adding the sauce. And the sauce is homemade. The meat is (self) served in roasters (but we do have someone on stand-by for kids or anyone who doesn't want to build their own. We have onion slices, pickle spears, jalapeno slices along with 2 styles of mustard, BBQ sauce and plastic forks. Some people prefer an open face sandwich which is a great option. Some will put the meat into hot dog buns, and some folks will add some of the meat atop their hot dog.
This is more convenient than grilling burgers, the food stays warmer, and people have several options instead of just two. One year a guy said "I haven't had a sloppy Joe in 30 years", the guy ate 3 and a couple of hours later took 2 more in a go-box, which by the way we always have on hand.
The recipe is on my cookin's site, or I can give you the direct link if you are interested.
