You need a third roaster- one for each entree- for amounts. I would make 50 shrimp entree, 50 turkey and 35 third entree using my quantity tables.

Ground Beef
Cheese
Lettuce
Tomatoe
Sour Cream
Onions

For make it yourself tacos, you need the same amount of toppings per person as for the baked potato bar- there is a very explicit and complete chart that includes all the usual toppings. See the baked potato bar info sheet listed on Big Pots.

Be SURE you use only heavy duty outside weight cords if you need extension cords, one for each roaster. Try to plug themin to different electric circuits- when they all kick on, they can overload your circuits.

Reheating, keep the heat low (300)and the food tightly covered to avoid drying out. Get an instant read thermometer- as soon as the temp in the middle of the food is 180, turn down the heat to 200. Keep the lids on when people are not actually serving themselves.

The chicken is a separate situation. If the chicken is frozen, it needs to go in the fridge to thaw, allow 24 hours for each 5-6 pound package (it can hold in the fridge up to 48 hours thawed- so start earlier rather than later). Reheat it tightly covered or in foil in a real oven at 350-400, then when hot transfer to the roaster at 200. See timing below.

You don't say exactly the shrimp is prepared ahead (in size/type pan) or whether it is all to be boiled fresh and transferred to roasters after cooking. If frozen casseroles, then like the chicken, it needs to be thawed under refrigeration.

An oven full of cold food takes about an hour to reheat- judge by the volume of food you have, how many times you need to fill the oven. Reheat the chicken first, it hold better than the shrimp.

So you have some calculating to do about the oven and reheating before you can do the time table. You DO turn the roasters on to preheat about 1/2 hour before they are filled.