Can a cake be baked and frosted (with a cream cheese frosting) and then frozen for a week to be decorated at a later time? If so, what is the best way to wrap it and defrost it so it isn't dry or mushy?

Carrot cakes (with cream cheese frosting) are shipped by wholesalers all the time and frozen for longer than a week. Multiple undecorated cakes are frozen in a cardboard box with dividers, and decorated cakes are frozen in individual domes. Wrapping them to be airtight isn't a main concern (unless they need to be frozen for months), the icing seals the cake so it can't dry out, and the board/plate it's on prevents the air from getting to the cake from the bottom. They can be thawed in the box or dome they're provided in, or can be removed from the container to thaw on the counter. You shouldn't have any problem with dry or mushy.