According to the USDA a cake can be safely frozen for up to 12 months if wrapped properly (and airtight) and it follows the non-potentially hazardous food rules (also a good thing to keep in mind if you have a bride and groom who want to save their cake top for the 1st anniversary). Food cannot be safely re-frozen once it is thawed. That said, however, I would never do that for a paying customer, just in case the integrity of the cake becomes compromised or it were to absorb freezer flavors – (a few days may be okay, especially if you are doing a carved cake) but there are no guarantees there. I have frozen crumb coated cakes 1-2 weeks before for my children’s birthdays without a problem at all. I just let them thaw in the fridge overnight (still wrapped in 2 layers of plastic wrap) and then ice them with a final coat of buttercream the next morning (and fondant if I am using it). To make a giant cupcake I use a 6” round (2-layers) (for the bottom of the cupcake) and an oven safe pyrex or the Pampered Chef glass mixing bowl is the perfect size for the top, and it is already rounded, so no carving involved.