You said most important thing. However, what you're missing is that Fox can barely navigate Stan's time at Timely Comics due to them not having the Captain America rights. And the furthest they can really go into Marvel is the Fantastic Four. Right now they'll have an improbable time mentioning anyone else other than X Men. So you're largely looking at a depiction of Stan without his creations which is like making a movie about Victor Frankenstein without his monster.
Lol maybe that's why Fox just acquire the film right just so Marvel Studio and Sony can't get it (since as you said, they don't like each other)