In a medium bowl, sift together the rice, tapioca and buckwheat flours, the baking soda, xanthan gum, ginger, cinnamon, pumpkin pie spice and salt. Whisk until well blended, and set aside.
In a large bowl, use an electric mixer on medium speed to cream the butter with the brown sugar until the mixture is light, airy and pale tan, about 3 minutes. Add the egg and mix again on medium until incorporated, about 1 minute. Add the molasses and vanilla, and mix again at medium speed for another minute. Add half the dry ingredients and mix on low until incorporated. Add the second half of the dry ingredients and mix on low until the dough comes together in small clumps. (The dough will resemble thick brownie batter.) If the dough is too wet and not clumpy, add another tablespoon or two of rice flour. Using your hands, bring the dough together into a ball and knead for 1 minute, or until you can make a smooth ball of dough. Shape the dough into a disk and place in a resealable plastic bag, removing excess air. Chill the dough in the refrigerator for about 1 hour. (If the dough chills much longer than an hour, let it sit on the counter for about 10 minutes to soften before proceeding.)
When ready to make the cookies, adjust oven racks to the top and bottom thirds and preheat the oven to 350 degrees F. Line two baking sheets with parchment.
Divide the dough in 3 equal portions. Refrigerate two portions while you work on the first. Roll the dough out to a 1/8-inch thickness. (Best method for GF cookies is to use parchment paper barely dusted with rice flour on the top and bottom of the dough - this avoids needing to use a lot of extra bench flour to keep the dough from sticking to the counter). Use cookie cutters to cut out gingerbread men. You should be able to cut out 5 to 6 gingerbread men from each third of the dough, assuming they are 3 inches tall. Gather and re-roll the scraps. (Don't worry about overworking the dough, there isn't any gluten.)
Arrange the gingerbread men on the prepared baking sheets about 1 inch apart and bake until the edges just begin to take on golden color, 8 to 10 minutes. (For softer cookies, cook a minute or 2 less.) Let the cookies cool for a minute on the cookie sheet, and then remove and place on a cooling rack to cool completely. Let the baking sheets cool completely.
Repeat the process for the remaining dough portions.
Once completely cooled, decorate the cookies with colored Easy Royal Icing, along with candies, nuts and sprinkles.
In a medium bowl, use an electric mixer on low speed to mix the egg whites until frothy, about 2 minutes. Add the orange juice and vanilla and mix again until blended. Sift in the confectioners' sugar, 1 cup at a time, and then mix on low speed until incorporated. After the third cup of sugar is added, keep mixing until the icing is smooth, thick and shiny, about 2 more minutes. (Add an extra tablespoon or 2 of confectioners' sugar if the icing seems runnier, like a glaze.) Divide into 2 or 3 portions, add desired amount of food coloring and mix well.
Fill a few tablespoons of royal icing in the corner of a resealable plastic bag, snip the tip and draw (or spread the icing with a paintbrush) onto the cookies (thin with a drop or 2 of extra juice). Chill the cookies in the refrigerator for a few minutes to harden the icing.
If not coloring the icing, use lemon juice instead of orange juice and omit the vanilla.