I was never a big FF guy in 616 canon, so I really only know the broad strokes of the book.
I think one of Reed's most constant defining characteristics is a bit of arrogance about how smart/right he usually is. Similar to Dr Strange in that way?
I think so. I didn't read FF regularly, but was generally familiar with them. My sense was that yeah, Reed could be arrogant about his ability to use science to solve problems, the same way Strange could be arrogant about magic solving problems.
But also, stylistically, the characters have changed a lot over time. I dunno, I'm just saying that there's no one single "right" version of Reed.
I think you need to tick certain boxes, some of which are explicit, and some of which are simply necessary for the story to work.
So, on the explicit side, he's gotta be a science dude, he's gotta be brilliant but maybe a bit arrogant. I mean, its his arrogance that gets them all their powers anyway, right? So, that needs to be there to some degree. Narratively, this gives you an edge for your character, which makes them interesting. If he's basically just Ward Cleaver with stretchy abilities, that's a snore.
You also need something in the core of who he is -- of who each of the characters are, really -- that compels them to be heroic. I mean, what makes them say "We're going to use these abilities to do good"? Why would they do that? That needs to be grounded in their characters, and not merely left to their position as "These are the heroes, so they do hero stuff."
What I think could make for the most interesting aspects of this is the tension between Reed and Ben, and again what compels each to be a hero. I would expect Reed to feel IMMENSE guilt about Ben. And I would expect Ben to feel IMMENSE rage about the underlying unfairness of being the only physically disfigured of the quartet. Everyone else can live glamorous, happy lives, but Ben (who appears to be an astronaut already) is reduced to a
thing. A monster. If this ends up being juxtaposed against him having been viewed as a national hero and kind of a ladies man previously, that's even worse for him. So what makes him decide to go do good? Loyalty to his family? The love of a good woman (e.g., Alicia Masters)? Something else? I think that's worth exploring.
I mean, you can go deep with each of these characters if you really care to. Sure, they can be handled at a very surface level (Johnny is just the annoying kid brother, or the hotshot hothead, or whatever; Sue is just "the girl"), but you can also play with those 1960s archetypes and try to get to the real people behind them. Maybe Johnny is a hotshot and a wiseass because nobody takes him seriously, and he feels like he has something to prove living in the shadow of these brilliant people. Maybe Sue chafes against the sexual politics of the 1960s that reduce her to "the girl" when she's a woman and brilliant mind in her own right. There's a ton here you can play with. Even moreso if this starts as a period piece and then ends up with them time-jumping to the present.
