For a long time i have thought that Mospeada has a pretty logical set up for a trilogy.
First movie starts with a bang, character and story into thru the Mars assault force, protagonist winds up on a journey with more character intros, ends with a bang acquiring protoculture fuel, new alpha and a victory for the hero's.
2nd movie more journey, more backstory and development of the Invid, enter Marlene and love interest, end in a logical place like Denver or New York.
3rd movie, moving towards final objective, resolve all the love interests, ends in big victory for the hero's.
It's not to unlike, structurally anyway, Star Wars.