Mr Fantastic has a really goofy power-set, that makes it difficult for cgi etc.
Invisible Woman - I'd be tempted to make her psychic. Let her be a telekinetic with latent telepathy that makes people think she's invisible.
Human Torch - pyrokinetic.
I'd actually do what has been suggested before - do a Doom movie. Show a man travelling the world mastering magic and technology in an attempt to save his mother's soul and free his country from tyranny. Show it as a 'Batman Begins' movie.
Showcase Reed being his intellectual peer, showcase Ben being his physical peer.
Then let him cast his battle armour as he attacks the Latvarian ministry. Allow him to sever ties and sell his girlfriend's soul to amass mystical power. Initially show him sympathetic. Let a subplot be his extra dimensional warping project for military purposes which Reed argued against.
Once the country is his, then show a news report where Reed has used his research to search the skies and gain the power, Doom has been forced to amass himself whilst they gain it in a freak accident. Whilst Reed genuinely wanted the project to explore, Doom sees it as a power grasping project.
As Doom conquers Latveria, allow him to reflect on the sacrifices he has made to become the most powerful person on the planet.
Have the F4 shown as Ben, having military connections, becoming an Air Force Major, with Reed being a multiple Phd.
Maybe downplay Reed into being a true shape-shifter, rather than being all elasticity.
Due to Marvel's recent IronDoom run, Doom will likely now be portrayed as a powerful anti-hero rather than a villain in the MCU. This complicates things a bit for bringing back the FF. They may initially oppose him, but they will have Doom walk that line between hero and villain. He'll do the wrong things but for perhaps good reasons, etc.
They had him doing this when he was babysitting Val. He's done this before many times. All his past atrocities will be re-spun as him being evil against worse evil! Sort of The Punisher on steroids. Doom is fights evil with evil. I don't see Doom as a villain any longer. Rather, a vigilante of epic proportions.