Make sure you check out my previous post and give me your feedback. In the meantime, I have discovered a technique of creating a sky by applying an envSky texture to a camera and then adjusting the density of the clouds, along with Sun Brightness and Sky colouring. This means that I can simply apply and keyframe animate a sky texture (either day or night) once the set decoration and camera set-up has been done; without the need for further modelling.
I have done a basic test of a sun setting, using envSky. It is only very quick but let me know if you think this works well or not.