Can you help me analyse this image? I am looking for how the image highlights the internal and external factors that impact Macbeth's actions in...

I think you have a good start.  I would agree with your observations, and add to them:

The fire is very significant.  In the image, it is literally inside Macbeth.  It is consuming him from within, just as his ambition, jealousy and later paranoia consume him from within.  First, these qualities lead to his moral disintegration, and eventually his physical death.  Once a fire is started, it tends to spread out of control.  That is what happens to Macbeth.  Once he starts on the path of illicit violence, his choice sets in motion forces both within and outside of himself that he cannot control. 

Note also that the fire is burning in the background of the battle scene.  It is consuming Scotland as well as Macbeth.  This is appropriate, because Macbeth and Lady Macbeth between them manage to do a lot of damage to the whole country.  So, the fire is an internal force that eventually becomes an external one when the inner burning starts to have outer effects.  

I am not sure the battle scene is showing Macbeth's glorious past as a soldier.  It may be the final battle in which Macbeth meets his end, to the great loss of Scotland. 

Note that in the image, almost every other image is "inside" Macbeth.  I think this suggests that they are almost all internal forces.  Their influence interacts with Macbeth's secret desires to cause him to take the actions he does.  

For example, the witches give an ambiguous prophecy which turns out not to be true in the sense that it first appears.  But Macbeth, hearing it through the filter of his pride and ambition, takes the prophecy as a license to go ahead with his coup.  

Similarly, Lady Macbeth (note the cold look on her face) influences her husband by giving him a rationale or justification for acting out his darkest desires.  He would not have given in to her urging unless there was a similar desire in himself, alongside his conscience which initially held him back. 

Not having seen the movie, I am not sure whether Banquo appears in this image.  His ghost might be suggested by the ruin or graveyard that is visible behind the witches, or even by the stained-glass window at the top of the image. 

I assume that the figure on horseback looking out over a cliff is Macbeth himself, but it could possibly be Banquo.  Both are, in a sense, in a position of looking out over Scotland (either to rule or seek what is best for Scotland), and both find themselves poised on the edge of destruction.

Hope this helps.