I agree with others...a taco bar or the walking tacos (to reduce costs you can just have baggies and the larger bags of doritoes....the smaller bags of chips could prove costly????)
For the vegetarian (and others) get black beans...keep warm in a smaller crock pot, and make your meat ahead of time and keep warm in a larger crock pot (we buy a huge thing of taco seasoning at Sams...dry mix you add with water to the burger..very inexpensive and if you do tacos or taco salad alot like we do....very economical).
Last weekend we had a surprise 60th for my FIL...and we kept the cold things cold by having a very small kiddie swimming pool filled with ice..and the bowls of cold things set into the ice....stayed cold for many hours!
So meat, black beans, salsa, sour cream, shredded lettuce, cheese, tomoatoes, onions, black olives, guacamole, chips (or hard and soft shells if ya go that way)...baggies if ya do the walking variety...or toss away bowls and have it be a taco salad deal (lettuce is cheap).....sounds yummy......
Maybe do a whole Fiesta thing.......sounds easy and fun!
My problem with the BBQ parties (we have done several over the years) is that my husband never gets to participate much in the party cuz he spends the whole thing cooking or whatever...watching the grill...never a good combo with little kids running around (a hot grill).....
Have a great party!!!!