You just wowed me, has it really been 33 years?
Well it truly seems that enough time has passed that this project can proceed like a fresh idea, not tied to the animated movie at all. That gives everyone involved the freedom to re-imagine every aspect of the story.
Your cast selection listed above is well balanced, you've considered how the characters would play against each other. I like how the emphasis remains on the voice, get characters that sound right and you can alter appearance as needed.
For some reason "The Last Unicorn" makes me think of Middle-earth.