I think the Skrull secret invasion begins due to the snap: either they target the 50% who have been revived, as any weird behaviour could be put down to PTSD / a side-effect of being dusted; or they began during the 5 year gap when the world was in chaos and politicians etc disappeared. I think the former is more likely.
I also think Black Panther 2 will deal with the ramifications of him being gone for 5 years: again, we got a line early on about world governments falling into chaos and Wakanda should be no different.
Spider-Man: FFH will deal with both the new age gap (seeing some classmates already working / in college) and in him looking for a new father figure to replace Stark, and from the trailer it seems like it will be a choice between Mysterio or Hogan. I would guess, if it's true that the Chameleon is part of Mysterio's gang, that we get an Edward Scissorhands type plot where the aim is to steal something and frame Spider-Man for it, leading into the public / Bugle hating him. I would guess that Hogan will die as a result, ending Favrau's involvement as an actor in the series and giving Spidey yet another father figure death (or he saves him, to subvert that).
GOTG 3 I think will deal with bringing Gamora back. The past Gamora isn't "our" Gamora; our Gamora is still dead and in the soul stone. But I think the conceit will be that, they are two bodies from two different timelines, but in each timeline / reality they only have one soul. So past Gamora will somehow merge with main timeline Gamora, as the two souls can't exist simultaneously in the same timeline.
Finally, with alternate timelines now in play, and The Eternals on the release slate, I think it's a foregone conclusion that Kronos will play a big part in that, or at least be an end credits scene setup in that film
