Even though this is an older thread it looks like people are still asking similar questions so I thought I'd throw my opinion into the mix.
Mustafar is one of the easier environments in Star Wars to recreate because all of the elements which make up the landscape exist in real life, albeit on a smaller scale. You should be able to create pretty convinving backdrops by getting plenty of reference pictures of cliffs and rocks (scale's not terribly important as you're going to composite them anyhow and that'll mean re-sizing and stuff. Then it's just a case of grading and compositing all of the reference plates into a realistic looking background. As well as using your own pictures you can get stock pictures of lava flows (or just google them if you really want) and build your "cliffs" around them.
Once you have a basic background you'll probably want it animated which isn't all that difficult when you think about it as the background will need to be blurred slightly if the background is in focus for a realistic composite due to depth of field and the like...which means that you can cheat. If you create some artificial lighting (such as with the neon light engine in EL) and have it moving appropriately then you'll be able to sell the effect that the lava flows are moving pretty well. Then add create some lava spurts in your favourite particle engine and comp those in as well. Add blur and composite.
I'm planning to have a tinker with this basic method and write it up tutorial-wise if anyone would be interested (and if it looks any good) but I think it should do ok.
EDIT: Something I made a few years ago just to prove that the scale of your reference pics doesn't really matter (the lava was a really close up pic but looks like a long, winding stream here).