Sift all-purpose flour and cake flour into a large bowl. Whisk in baking powder, baking soda, and salt. Set aside.
In a small bowl, whisk buttermilk and lime juice. Set aside.
In a food processor, pulse together the sugar and lime zest until finely ground. In an electric mixer (or with electric beaters in a large bowl), whip the sugar/lime zest mixture with butter until light and fluffy. Scrape down the sides and bottom of the bowl while mixing to ensure it is all blended. Gradually add eggs and egg whites one at a time and then vanilla. Mix well.
Add 1/3 of flour mixture to the batter and mix just until combined, then add 1/2 of buttermilk mixture to the batter and mix. Repeat ending with last 1/3 of flour mixture.
Divide batter among 24 muffin cups lined with cupcake liners.
Bake for 18-20 minutes or until toothpick inserted in the center of a cupcake comes out clean.
Cool for 5 minutes in muffin tin, then transfer to a wire cooling rack and add simple syrup.
Whisk lime juice and sugar until the sugar is dissolved. With a pastry brush, brush syrup over warm cupcakes. Allow cupcakes to cool completely.
Whip butter in a mixer until light and fluffy. Mix in 1/2 cup powdered sugar, then maraschino cherry juice and red food coloring. Slowly add remaining 4 1/2 powdered sugar and whip until well blended. If necessary, add more powdered sugar to reach desired consistency.
Spread or pipe frosting on completely cooled cupcakes.