How do I cook and hold pasta for 200 people?
The common method would be to cook the pasta in advance, then shock it in cold water to stop the cooking before draining and refrigerating it.  You would then heat it up in boiling water for about 20 seconds just to heat it through.

You would just need a portable burner to keep a pot of water boiling for service.



On the other hand, 20 pounds of pasta for 200 people is a portion size of only about 1.5 ounces per person.   That is a very, very small portion, less than side-dish sized.

For side dishes, 2 ounces of pasta is more typical.   If you are serving it as a main dish, 4-5 ounces would be more typical.

(Weights are for dry pasta.)