Welcome to the Cake Decorators Q&A

Can this all be made out of buttercream and Jam Or Buttercream and Jam and then Ganache on the outside Or should it all be made out of Ganache because of the structure of the cake ?

Hi Sky Cake

Filling the cake with ganache will be better for keeping the structure more stable but it is personal choice as long you use ganache for the crumbcoat. Ganache does give a far superior stability. Try to avoid using excessive amounts jam if not filling with ganache. Jam, paired with buttercream will make the layers slip and slide and altering the shape of the car.

Hope this helps and happy decorating!