A simple question, do you think the strings on Starman are actual strings, or a Mellotron (or both!)?

I say they're real strings. Listen to them, they're far too expressive to be a clunky, out-of-tune, Mellotron.

Plus, even Mick Ronson said (on a video I saw on YouTube) they're strings. His story was essentially that David Bowie told Mick to come up with an arrangement but he had never written for anything other than guitars so had to learn how just by getting on and doing it! Sounds to me like he did a pretty good job...