1.)
First. begin with Secret Wars to explain the mergers of the Marvel & X-Men universes. Rather than just have mutants showing up without any explanation, just use Galactus in place of The Beyonder to be the one to bring everybody together. Then have the necessary exposition narrated by Uatu The Watcher to help ease the confusion for fans who aren't die-hard comic heads whilst also introducing a brand new character.
Galactus works so well because every action/hero/etc movie needs a villain more powerful than wh0ever came before. This is partially why Justice League was so underwhelming because Steppenwolf would've stood no chance against Doomsday.
Galactus is perfectly ideal for this because he's one of the few characters out there in Marvel powerful enough for such a feat AND one who can literally toy around with Thanos like a child.
2.) Now with Norrin Radd introduced in Secret Wars we can get a Silver Surfer movie with Rami Malek
3.): And have all this tie-in to a proper Dr. Doom solo movie with Madds Mikkelsen
4.) NOW with all the pieces in play we can get a solid Fantastic Four movie once and for all. Maybe have the 2nd film end with Sue pregnant with Franklin Richards. This could then set up Infinity Wars Deluxe (much further down the line with the war with the celestials) or the Power Pack films.
Here's Franklin treating some Celestials like h0es
5.) While everything else is happening in space (we'll call it "cosmic marvel") now we bring out the big guns
Seriously imagine that scene playing out exactly like that but the shadowy figure bearing none other than Heisenberg's voice
While all this is going on in Earth I'm thinking the GOTG or wh0ever could be out in space doing the Annihilation story and meanwhile on Earth they're doing the "Dark Reign" storyline where Norman Osborn was in charge and given his own black-ops team of assassins. I could see someone like General Ross being like Amanda Waller being fed up and not trusting of heroes so he sanctions his OWN Thunderbolts behind everyone's back.
Then the next "Infinity Wars" can be when Franklin is all grown up and he and Galactus have to take down the Celestials.