I am making a S'mores Sandcastle cake for my kids 3rd and 5th birthday party. I am very much a beginner with all of it. My only question, however, is when to decorate and how to store it? 

     The party is on a Saturday. I want everything to be as fresh as possible without me rushing last minute (my mistake every year). I was thinking, I would bake the cakes on Thursday. Then, assemble and decorate on Friday evening. 

     So, I guess my question is.. Can I completely decorate a cake with icing and graham cracker crumbs, and then store it over night? ..and how should I store it? Uncovered in the fridge? freeze it in layers and then stack it the day of?

     I'm just trying to be as prepared as possible. Thanks in adavance! 

Bake the cakes now!  Torte, fill, and wrap in several layers of saran.  Thaw on the counter (still wrapped) and decorate on Friday.  As long as there's no perishable filling, I'd leave it in a box on the counter Friday night and until the party on Saturday!

AI'd bake the cakes early, as stated above but I'd split up baking and torting since your new. Bake cakes Monday or Tuesday, cover in Saran wrap (and foil) and stick in the freezer/fridge-it's easier to level and torte cakes when they're partially frozen (but you can skip this step).

Next day, Make BC. Torte, fill, and wrap...same as above thaw while covered so any condensation forms on foil/cling wrap.