Heat oven to 180°C (170°C for dark or nonstick pans). Grease or spray bottoms and sides of four 20cm square pans. In large bowl, beat 1 cake mix, 250ml of the water, 125ml of the oil and 3 eggs using electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Divide batter between 2 pans. Bake 2 pans at a time for 23 to 29 minutes (26 to 34 minutes for dark or nonstick pan) or until toothpick inserted in center comes out clean. Cool 10 minutes; remove from pans to cooling racks. Cool completely, about 30 minutes. Repeat with remaining cake mix, water, oil and eggs. Chill cooled cake in freezer 45 minutes before cutting, to reduce crumbs.
Spoon frosting into large bowl. Stir in enough food color until desired pink color.
Using serrated knife, cut off domed top from each cake so they will be flat when stacked. On tray, place 1 cake, cut side down; spread 75 grams frosting over top. Add second cake, cut side down; spread top with 75 grams frosting. Add third cake, cut side down; do not frost.
Cut fourth cake into quarters. Spread small amount of frosting on center of cake, about the size of a cake quarter. Place 1 quarter, cut side down, on top of frosting. Spread top of stacked cake quarter with 1 tablespoon frosting. Place second quarter on top of first quarter; spread top with 1 tablespoon frosting. Add third quarter; do not frost. Cut fourth quarter into quarters to create four 5cm squares. Spread a small dollop of frosting on the top center of the second tier of cakes. Place one 5cm piece on the center; spread top with frosting. Top with one more 5cm piece. (Discard remaining 2 pieces.)
Spread thin layer of frosting over layered cake to seal in crumbs. Freeze cake 30 to 60 minutes.
Frost pointed-end cones with frosting; roll in pink sugar. Frost cake with remaining frosting. Place 1 upside-down cone on each corner of the first cake layer and 1 on top cake layer for center steeple. Top each cone with a candy star.
Place sugar cubes around edges of the first and second layers. Top each of the 4 corner sugar cubes with a gum ball. Attach 2 cookies on one side of first layer to create doors. Cut 2 additional cookies to desired size for windows; place each cookie on opposite sides of doors.
Cut remaining cookie in half; place 1 half in center of second layer to create accent window. Pipe on window panes and doorknobs with white icing. Store loosely covered.