AI have a couple cakes for this weekend, one is a smash cake for a 1 year old. Can I frost the cake (using a crusting buttercream), go back the next morning and add the fondant decorations and finish off with the buttercream trim (again, crusting buttercream) on the lower and upper edges? All help appreciated, I was used to using a noncrusting buttercream but like the crusting better...

Yes, you can do exactly as you say!!! You can even prepare the fondant decos ahead. Put in closed container. I actually lay mine out on a white freezer paper  covered cake board,

, shiny side up. wrap with saran. place in fridge and when ready , place on cake. I do this with modeling chocolate decos also. this helps so much with time. hth

Great help!  I did my fondant decos ahead last time but didn't put them in the frig and I didn't have them shiny side up.....I had them shiny side down on my small rolling board in a ziplock on the sink....  Should I put them in the frig?  When I put them on the cake, the decos were room temp and cake was just out of the frig...it worked just fine but I'm always after whatever is better than fine....lol!