I commend you on doing something to help others! Is it going to be the only entree or will there be other stuff? An ounce of dry pasta will be around 3-4 oz cooked. Normally I'd plan on about 8 to 9 oz of cooked pasta + the sauce for a hearty entree. But I suppose that maybe these folks might eat a bit more than the average diner. Pasta is fairly inexpensive, I'd err on the side of having extra. On the low side I'd say go with at least 75 pounds of penne, uncooked weight. A hundred wouldn't be overkill; in banquets generally you include a 3% to 5% overage just in case. If you're using 200 pans you won't get more than a few pounds in a pan. I'd use a 400 or 600 pan (ie a full pan, 4" or 6" deep respectively).
Cook the pasta al dente (almost undercooked) to keep it from getting too mushy.
Cooking is, to me, just about the most fundamental way of relating to and serving our fellow humans. It's a noble endeavor. If you have any other questions post them here!