I never use icing sugar because it dries out the fondant :) I always use cornstarch. It doesn’t dry out the fondant and it’ll minimize the little cracks. I use a homemade duster so I won’t use to much cornstarch because there’s no need to.
To remove excess cornstarch I always use a big soft brush e.g. a powder brush normally used for make-up.
Shortening as Ann-Maries mentions is great to help with the little cracks and also to remove excess powder – but only if the brush doesn’t remove it.