I think you could get at least 15 covers from a no. 1 pan of arroz con pollo figuring two pieces of darkmeat per cover, i.e., 100 leg and thigh quarters. Separate the quarters into pieces and it allows for big eaters, small eaters and multiple trips through the buffet line. Arroz con pollo has the advantage of being one of those dishes which profits from holding and survives -- even thrives -- with reheating.
There are any number of strategies for when and where to cook, and how to reheat -- if necessary. Those depend on available facilities and equipment. Not to channel Shroomgirl or anything.
For what it's worth, there aren't many recipes for anything which feed 100 -- at least outside of institutions with specialized high-volume kitchens. Typical catering "recipes" are scaled for available cookware, serving pieces, stove and counter space, and multiplied to provide the necessary volume.
Your practice of banging out food by the pan is one of the very best ways to organize a catering job. But you need to overcome your shyness when it comes to large numbers of pans. If you're serving hot food from chaffers, there really isn't any better way to do it.
Hope this helps,