Will there be any minor antagonists?

[Ghost_Ultramantis]

I would go so far as to say that the Kaiju are the minor protagonists and the whole film sets up to reveal the major antagonists in the sequel.

Edwards has pretty much said this will be a self-contained film, not baiting a sequel. He might do one, but he prefers the "one film - one story" approach.

Star Wars was "self-contained" back in 1978. The new retconned origin is setting up for a much bigger story. This is the beginning of the LegendaryGoji franchise. Could I be wrong? Absolutely. Am I? Wait and see.

[Ghost_Ultramantis]

Again, Star Wars (Chapter 4) was a self-contained story. Lucas did not know if it would be an economic success to warrant the expansion on the backstories he had created at the time. Backstories...that organically grew into much more over time.

Edwards has ALREADY hinted at a possible sequel. Once successful, Lucas was able to indulge in a bit of romantic retelling of how his vision became reality...which it hasn't quite, because Disney bought the "final three", right?

Anyway, Legendary didn't go all in on this new Godzilla and create a reimagined universe just to make an awesome "One Shot". It absolutely must stand alone as a film, but to think Legendary doesn't have huge plans with Toho to develop a persistent world is just nuts. Lucas did it and Marvel is perfecting it. It could be episodic like Bond. Edwards could be burned out and tap out. Cranston and the rest might opt out. But big plans and stories, pending a home-run, have been in story development for a while. I'm sure Tull will have his own romantic retelling 10 years from now if it comes to fruition.

[Godzillasaurus]

I honestly don't think that calls for spoiler tags. Because it saves people who read it time when they try to watch through the credits for a stinger, and it will save the disappointment