This is the first time I've used a base tier of 18" and baked my layers in the half-round pan. I now have four half-cake layers.
My question is this: When using the half cakes, is there anything special I need to do after leveling besides butt them up against each other on the cake board, add filling, place other two half-cakes on top and crumb coat as one whole unit?
Nope, unless you'd like to rotate the top two halves so they aren't in the same direction as the two halves below. )
Definitely rotate so that all the cake seams are NOT in the same place.