I made a "3" as a 3 layer cake, starting with 12x15 sheets
I knew it had to serve 25+ and it was for family so I always go bigger. I made a few giant 3's on the back of wrapping paper to the size of the cake and then I cut up my templates so I could use the 12x15 sheet the most efficiently. My concern was that if the cake layers were all attached at the same curves, the cake would be less stable ( I had to drive it about 35 miles) so I cut the middle layer differently than the 1st and 3rd layer for more stability. I don't know if others would do it this way but it worked for me!