Not clear on how you are going to get the veggies cooked, and handling cooked meat and raw veggies together, especially with volunteers, is not a great plan, food safety-wise.

How about doing these foods fajita style, it uses the same amount of food, will taste MUCH better and be a lot less work. You can add tortillas, that small amount of carb would be very satisfying. Use half corn in case of gluten-free eaters.

Since this is a health conscious crowd, I would do 5/8 chicken, 3/8 beef instead of the usual, which is revers.

Good outline on fajitas and recipes on this site:
www.ellenskitchen.com/bigpots/plan/texmexfajitas.html

furit kabobs (watermelon, cantelope, strawberry, grapes); assuming you want 2 skewers per person, 8-10 pieces of fruit total, you can use the fruit tray page to decide how many melons, pounds of grapes and strawberries to buy. Again, cut up fruit is a great bacteria catcher. Those assembling must wear gloves, and it need to be chilled after cutting. I usually suggest fruit trays with just a few kabobs for garnish; keep better, people can take what they want (you would be surprised how many people can't eat strawberries), and the leftovers are more usable. One deluxe tray for 100 would be more than enough.