Just before serving, whip the cream until stiff. Spread over the pie, smooth into small swirls. A handy utensil for whipping cream is available in specialty cooking stores. ISI GmbH, Vienna, Austria makes a Coffee Cream Whipper which uses N20 chargers. It's faster than beaters or whisks and more fun, because everyone can swirl on their own cream from the dispenser, plus the cream stays fresh and usable in the refrigerator for several days.
Mexican limes are the same type of lime as Caribbean Key limes, small and very flavorful.
Limes originated on the Malay Peninsula, were cultivated in India and then imported to the New World during colonial times. Fresh limes will keep for a long time. Let the air circulate around them in a basket so they don't mold. When the skin dries to a hard shell, the juice is intact inside. Perhaps that's how they were carried on the sailing ships where they were used to prevent scurvy on long voyages.