AObviously, I'm new to cake decorating but giving it a try for my daughter's bday. Why do you put buttercream frosting under fondant? Could you use cream cheese frosting? Also, I live in a warm climate and last time I made buttercream frosting it was kind of melting more as I used it. Any help would be greatly appreciated!

well you need something for the fondant to adhere it to the cake. old school decorators used a thin layer of apricot jam. you definitely need to work in a cooler environment with buttercream, but you can also chill your cake before applying the fondant. 

You need something to glue the crumbs down.  Then you need to make a nice smooth layer for the fondant to stick to.

Best to test your cream cheese frosting under fondant, some of the recipes have a significant amount of liquid and the fondant soaks up that water kinda fast.  Make sure you use full fat cream cheese, it has less water.

Another reason is some people don't like fondant and will peel it off. If there's nothing under your fondant, they'll get a naked cake to eat

Ganache holds up well to heat. Have you thought about using cream cheese buttercream as a filling then white chocolate ganache, flavored as desired, as the layer that meets your fondant? After the ganache sets, you can lightly mist/brush it with water or brush with melted preserves to give the fondant something to adhere to.

AThanks so much for your replies. Totally makes sense! I think I'm ready to give it a go!

Great! Let us know how everything turns out for you