My favourite part of cake decorating is creating detailed fondant sculptures. However, I'm still new at this and trying to figure out when to use fondant, gumpaste or a mixture of both. I really take my time when sculpting, so I prefer the longer open-time of fondant, but I like the hardness of gumpaste to make moving the sculptures onto the cake easier. Is there some kind of rule of thumb as to when to use which one...and in what proportion? All and any advise welcome!

50/50 gumpaste and fondant - you can adjust then proportions till you are happy. Or - you can add a teaspoon of tylose powder to about half a pound of fondant, mix well and wrap tighly in plastic wrap until you are ready to use

i like just adding tylose to fondant.
it's nice to not have to make both fondant and gumpaste and, also, it feels i don't need to work at matching the colour of my cake since i'm just using fondant from it.