I don’t crumb coat in buttercream. I use ganache to crumbcoat in but I let my ganache sit in the fridge overnight before I put my fondant on. And usually I puit my fondant on right after I take it out of the fridge.
As for the cracking not sure if this will help or not.. it seems everyone has their own techniques and favorite brands. I used to use powdered sugar with my satin ice roll out but that was when i got tons of cracking. It dried the fondant out to quickly.
The best success I have has was with sweetwise’s MAT. It gets seasoned with shortening once and then you roll between 2 sheets of vinly. Basically it keeps the air away from the fondant while rolling so it does not dry it out. And I don’t have to handle it at all. I use the vinyl to help get the rolled fondant on the cake.